Hi,
On Wed, 28 Feb 2024 at 14:42, Nazir Bilal Yavuz <byavu...@gmail.com> wrote:
>
>
> The new version of the streaming read API [1] is posted. I updated the
> streaming read API changes patch (0001), using the streaming read API
> in ANALYZE patch (0002) remains the same. This should make it easier
> to review as it can be applied on top of master
>
>
The new version of the streaming read API is posted [1]. I rebased the
patch on top of master and v9 of the streaming read API.
There is a minimal change in the 'using the streaming read API in ANALYZE
patch (0002)', I changed STREAMING_READ_FULL to STREAMING_READ_MAINTENANCE
to copy exactly the same behavior as before. Also, some benchmarking
results:
I created a 22 GB table and set the size of shared buffers to 30GB, the
rest is default.
╔═══════════════════════════╦═════════════════════╦════════════╗
║ ║ Avg Timings in ms ║ ║
╠═══════════════════════════╬══════════╦══════════╬════════════╣
║ ║ master ║ patched ║ percentage ║
╠═══════════════════════════╬══════════╬══════════╬════════════╣
║ Both OS cache and ║ ║ ║ ║
║ shared buffers are clear ║ 513.9247 ║ 463.1019 ║ %9.9 ║
╠═══════════════════════════╬══════════╬══════════╬════════════╣
║ OS cache is loaded but ║ ║ ║ ║
║ shared buffers are clear ║ 423.1097 ║ 354.3277 ║ %16.3 ║
╠═══════════════════════════╬══════════╬══════════╬════════════╣
║ Shared buffers are loaded ║ ║ ║ ║
║ ║ 89.2846 ║ 84.6952 ║ %5.1 ║
╚═══════════════════════════╩══════════╩══════════╩════════════╝
Any kind of feedback would be appreciated.
[1]:
https://www.postgresql.org/message-id/CA%2BhUKGL-ONQnnnp-SONCFfLJzqcpAheuzZ%2B-yTrD9WBM-GmAcg%40mail.gmail.com
--
Regards,
Nazir Bilal Yavuz
Microsoft
From 7278c354d80e4d1f21c6fa0d810a723789f2d722 Mon Sep 17 00:00:00 2001
From: Thomas Munro <thomas.mu...@gmail.com>
Date: Mon, 26 Feb 2024 23:48:31 +1300
Subject: [PATCH v3 1/2] Streaming read API changes that are not committed to
master yet
Discussion: https://www.postgresql.org/message-id/CA%2BhUKGJkOiOCa%2Bmag4BF%2BzHo7qo%3Do9CFheB8%3Dg6uT5TUm2gkvA%40mail.gmail.com
---
src/include/storage/bufmgr.h | 45 +-
src/include/storage/streaming_read.h | 50 ++
src/backend/storage/Makefile | 2 +-
src/backend/storage/aio/Makefile | 14 +
src/backend/storage/aio/meson.build | 5 +
src/backend/storage/aio/streaming_read.c | 678 +++++++++++++++++
src/backend/storage/buffer/bufmgr.c | 706 ++++++++++++------
src/backend/storage/buffer/localbuf.c | 14 +-
src/backend/storage/meson.build | 1 +
src/backend/utils/misc/guc_tables.c | 14 +
src/backend/utils/misc/postgresql.conf.sample | 1 +
doc/src/sgml/config.sgml | 14 +
src/tools/pgindent/typedefs.list | 2 +
13 files changed, 1309 insertions(+), 237 deletions(-)
create mode 100644 src/include/storage/streaming_read.h
create mode 100644 src/backend/storage/aio/Makefile
create mode 100644 src/backend/storage/aio/meson.build
create mode 100644 src/backend/storage/aio/streaming_read.c
diff --git a/src/include/storage/bufmgr.h b/src/include/storage/bufmgr.h
index d51d46d3353..1cc198bde21 100644
--- a/src/include/storage/bufmgr.h
+++ b/src/include/storage/bufmgr.h
@@ -14,6 +14,7 @@
#ifndef BUFMGR_H
#define BUFMGR_H
+#include "port/pg_iovec.h"
#include "storage/block.h"
#include "storage/buf.h"
#include "storage/bufpage.h"
@@ -133,6 +134,10 @@ extern PGDLLIMPORT bool track_io_timing;
extern PGDLLIMPORT int effective_io_concurrency;
extern PGDLLIMPORT int maintenance_io_concurrency;
+#define MAX_BUFFER_IO_SIZE PG_IOV_MAX
+#define DEFAULT_BUFFER_IO_SIZE Min(MAX_BUFFER_IO_SIZE, (128 * 1024) / BLCKSZ)
+extern PGDLLIMPORT int buffer_io_size;
+
extern PGDLLIMPORT int checkpoint_flush_after;
extern PGDLLIMPORT int backend_flush_after;
extern PGDLLIMPORT int bgwriter_flush_after;
@@ -158,7 +163,6 @@ extern PGDLLIMPORT int32 *LocalRefCount;
#define BUFFER_LOCK_SHARE 1
#define BUFFER_LOCK_EXCLUSIVE 2
-
/*
* prototypes for functions in bufmgr.c
*/
@@ -177,6 +181,42 @@ extern Buffer ReadBufferWithoutRelcache(RelFileLocator rlocator,
ForkNumber forkNum, BlockNumber blockNum,
ReadBufferMode mode, BufferAccessStrategy strategy,
bool permanent);
+
+#define READ_BUFFERS_ZERO_ON_ERROR 0x01
+#define READ_BUFFERS_ISSUE_ADVICE 0x02
+
+/*
+ * Private state used by StartReadBuffers() and WaitReadBuffers(). Declared
+ * in public header only to allow inclusion in other structs, but contents
+ * should not be accessed.
+ */
+struct ReadBuffersOperation
+{
+ /* Parameters passed in to StartReadBuffers(). */
+ BufferManagerRelation bmr;
+ Buffer *buffers;
+ ForkNumber forknum;
+ BlockNumber blocknum;
+ int16 nblocks;
+ BufferAccessStrategy strategy;
+ int flags;
+
+ /* Range of buffers, if we need to perform a read. */
+ int16 io_buffers_len;
+};
+
+typedef struct ReadBuffersOperation ReadBuffersOperation;
+
+extern bool StartReadBuffers(BufferManagerRelation bmr,
+ Buffer *buffers,
+ ForkNumber forknum,
+ BlockNumber blocknum,
+ int *nblocks,
+ BufferAccessStrategy strategy,
+ int flags,
+ ReadBuffersOperation *operation);
+extern void WaitReadBuffers(ReadBuffersOperation *operation);
+
extern void ReleaseBuffer(Buffer buffer);
extern void UnlockReleaseBuffer(Buffer buffer);
extern bool BufferIsExclusiveLocked(Buffer buffer);
@@ -250,6 +290,9 @@ extern bool HoldingBufferPinThatDelaysRecovery(void);
extern bool BgBufferSync(struct WritebackContext *wb_context);
+extern void LimitAdditionalPins(uint32 *additional_pins);
+extern void LimitAdditionalLocalPins(uint32 *additional_pins);
+
/* in buf_init.c */
extern void InitBufferPool(void);
extern Size BufferShmemSize(void);
diff --git a/src/include/storage/streaming_read.h b/src/include/storage/streaming_read.h
new file mode 100644
index 00000000000..7991402631a
--- /dev/null
+++ b/src/include/storage/streaming_read.h
@@ -0,0 +1,50 @@
+#ifndef STREAMING_READ_H
+#define STREAMING_READ_H
+
+#include "storage/bufmgr.h"
+#include "storage/fd.h"
+#include "storage/smgr.h"
+
+/* Default tuning, reasonable for many users. */
+#define STREAMING_READ_DEFAULT 0x00
+
+/*
+ * I/O streams that are performing maintenance work on behalf of potentially
+ * many users.
+ */
+#define STREAMING_READ_MAINTENANCE 0x01
+
+/*
+ * We usually avoid issuing prefetch advice automatically when sequential
+ * access is detected, but this flag explicitly disables it, for cases that
+ * might not be correctly detected. Explicit advice is known to perform worse
+ * than letting the kernel (at least Linux) detect sequential access.
+ */
+#define STREAMING_READ_SEQUENTIAL 0x02
+
+/*
+ * We usually ramp up from smaller reads to larger ones, to support users who
+ * don't know if it's worth reading lots of buffers yet. This flag disables
+ * that, declaring ahead of time that we'll be reading all available buffers.
+ */
+#define STREAMING_READ_FULL 0x04
+
+struct StreamingRead;
+typedef struct StreamingRead StreamingRead;
+
+/* Callback that returns the next block number to read. */
+typedef BlockNumber (*StreamingReadBufferCB) (StreamingRead *stream,
+ void *callback_private_data,
+ void *per_buffer_data);
+
+extern StreamingRead *streaming_read_buffer_begin(int flags,
+ BufferAccessStrategy strategy,
+ BufferManagerRelation bmr,
+ ForkNumber forknum,
+ StreamingReadBufferCB callback,
+ void *callback_private_data,
+ size_t per_buffer_data_size);
+extern Buffer streaming_read_buffer_next(StreamingRead *stream, void **per_buffer_private);
+extern void streaming_read_buffer_end(StreamingRead *stream);
+
+#endif
diff --git a/src/backend/storage/Makefile b/src/backend/storage/Makefile
index 8376cdfca20..eec03f6f2b4 100644
--- a/src/backend/storage/Makefile
+++ b/src/backend/storage/Makefile
@@ -8,6 +8,6 @@ subdir = src/backend/storage
top_builddir = ../../..
include $(top_builddir)/src/Makefile.global
-SUBDIRS = buffer file freespace ipc large_object lmgr page smgr sync
+SUBDIRS = aio buffer file freespace ipc large_object lmgr page smgr sync
include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/storage/aio/Makefile b/src/backend/storage/aio/Makefile
new file mode 100644
index 00000000000..bcab44c802f
--- /dev/null
+++ b/src/backend/storage/aio/Makefile
@@ -0,0 +1,14 @@
+#
+# Makefile for storage/aio
+#
+# src/backend/storage/aio/Makefile
+#
+
+subdir = src/backend/storage/aio
+top_builddir = ../../../..
+include $(top_builddir)/src/Makefile.global
+
+OBJS = \
+ streaming_read.o
+
+include $(top_srcdir)/src/backend/common.mk
diff --git a/src/backend/storage/aio/meson.build b/src/backend/storage/aio/meson.build
new file mode 100644
index 00000000000..39aef2a84a2
--- /dev/null
+++ b/src/backend/storage/aio/meson.build
@@ -0,0 +1,5 @@
+# Copyright (c) 2024, PostgreSQL Global Development Group
+
+backend_sources += files(
+ 'streaming_read.c',
+)
diff --git a/src/backend/storage/aio/streaming_read.c b/src/backend/storage/aio/streaming_read.c
new file mode 100644
index 00000000000..760a231500a
--- /dev/null
+++ b/src/backend/storage/aio/streaming_read.c
@@ -0,0 +1,678 @@
+/*-------------------------------------------------------------------------
+ *
+ * streaming_read.c
+ * Mechanism for buffer access with look-ahead
+ *
+ * Portions Copyright (c) 2024, PostgreSQL Global Development Group
+ * Portions Copyright (c) 1994, Regents of the University of California
+ *
+ * Code that needs to access relation data typically pins blocks one at a
+ * time, often in a predictable order that might be sequential or data-driven.
+ * Calling the simple ReadBuffer() function for each block is inefficient,
+ * because blocks that are not yet in the buffer pool require I/O operations
+ * that are small and might stall waiting for storage. This mechanism looks
+ * into the future and calls StartReadBuffers() and WaitReadBuffers() to read
+ * neighboring blocks together and ahead of time, with an adaptive look-ahead
+ * distance.
+ *
+ * A user-provided callback generates a stream of block numbers that is used
+ * to form reads of up to size buffer_io_size, by attempting to merge them
+ * with a pending read. When that isn't possible, the existing pending read
+ * is sent to StartReadBuffers() so that a new one can begin to form.
+ *
+ * The algorithm for controlling the look-ahead distance tries to classify the
+ * stream into three ideal behaviors:
+ *
+ * A) No I/O is necessary, because the requested blocks are fully cached
+ * already. There is no benefit to looking ahead more than one block, so
+ * distance is 1. This is the default initial assumption.
+ *
+ * B) I/O is necessary, but fadvise is undesirable because the access is
+ * sequential, or impossible because direct I/O is enabled or the system
+ * doesn't support advice. There is no benefit in looking ahead more than
+ * buffer_io_size (the GUC controlling physical read size), because in this
+ * case only goal is larger read system calls. Looking further ahead would
+ * pin many buffers and perform speculative work looking ahead for no benefit.
+ *
+ * C) I/O is necesssary, it appears random, and this system supports fadvise.
+ * We'll look further ahead in order to reach the configured level of I/O
+ * concurrency.
+ *
+ * The distance increases rapidly and decays slowly, so that it moves towards
+ * those levels as different I/O patterns are discovered. For example, a
+ * sequential scan of fully cached data doesn't bother looking ahead, but a
+ * sequential scan that hits a region of uncached blocks will start issuing
+ * increasingly wide read calls until it plateaus at buffer_io_size.
+ *
+ * The main data structure is a circular queue of buffers of size
+ * max_pinned_buffers, ready to be returned by streaming_read_buffer_next().
+ * Each buffer also has an optional variable sized object that is passed from
+ * the callback to the consumer of buffers. A third array records whether
+ * WaitReadBuffers() must be called before returning the buffer, and if so,
+ * points to the relevant ReadBuffersOperation object.
+ *
+ * For example, if the callback return block numbers 10, 42, 43, 60 in
+ * successive calls, then these data structures might appear as follows:
+ *
+ * buffers buf/data buf/io ios
+ *
+ * +----+ +-----+ +---+ +--------+
+ * | | | | | | +---->| 42..44 |
+ * +----+ +-----+ +---+ | +--------+
+ * oldest_buffer_index -> | 10 | | ? | | | | +-->| 60..60 |
+ * +----+ +-----+ +---+ | | +--------+
+ * | 42 | | ? | | 0 +--+ | | |
+ * +----+ +-----+ +---+ | +--------+
+ * | 43 | | ? | | | | | |
+ * +----+ +-----+ +---+ | +--------+
+ * | 44 | | ? | | | | | |
+ * +----+ +-----+ +---+ | +--------+
+ * | 60 | | ? | | 1 +----+
+ * +----+ +-----+ +---+
+ * next_buffer_index -> | | | | | |
+ * +----+ +-----+ +---+
+ *
+ * In the example, 5 buffers are pinned, and the next buffer to be streamed to
+ * the client is block 10. Block 10 was a hit and has no associated I/O, but
+ * the range 42..44 requires an I/O wait before its buffers are returned, as
+ * does block 60.
+ *
+ * IDENTIFICATION
+ * src/backend/storage/storage/aio/streaming_read.c
+ *
+ *-------------------------------------------------------------------------
+ */
+#include "postgres.h"
+
+#include "catalog/pg_tablespace.h"
+#include "miscadmin.h"
+#include "storage/streaming_read.h"
+#include "utils/rel.h"
+#include "utils/spccache.h"
+
+/*
+ * Streaming read object.
+ */
+struct StreamingRead
+{
+ int16 max_ios;
+ int16 ios_in_progress;
+ int16 max_pinned_buffers;
+ int16 pinned_buffers;
+ int16 distance;
+ bool started;
+ bool finished;
+ bool advice_enabled;
+
+ /*
+ * The callback that will tell us which block numbers to read, and an
+ * opaque pointer that will be pass to it for its own purposes.
+ */
+ StreamingReadBufferCB callback;
+ void *callback_private_data;
+
+ /* The relation we will read. */
+ BufferAccessStrategy strategy;
+ BufferManagerRelation bmr;
+ ForkNumber forknum;
+
+ /* Sometimes we need to buffer one block for flow control. */
+ BlockNumber unget_blocknum;
+ void *unget_per_buffer_data;
+
+ /* Next expected block, for detecting sequential access. */
+ BlockNumber seq_blocknum;
+
+ /* The read operation we are currently preparing. */
+ BlockNumber pending_read_blocknum;
+ int16 pending_read_nblocks;
+
+ /* Space for buffers and optional per-buffer private data. */
+ Buffer *buffers;
+ size_t per_buffer_data_size;
+ void *per_buffer_data;
+ int16 *buffer_io_indexes;
+
+ /* Read operations that have been started by not waited for yet. */
+ ReadBuffersOperation *ios;
+ int16 next_io_index;
+
+ /* Head and tail of the circular queue of buffers. */
+ int16 oldest_buffer_index; /* Next pinned buffer to return */
+ int16 next_buffer_index; /* Index of next buffer to pin */
+};
+
+/*
+ * Return a pointer to the per-buffer data by index.
+ */
+static void *
+get_per_buffer_data(StreamingRead *stream, int16 buffer_index)
+{
+ return (char *) stream->per_buffer_data +
+ stream->per_buffer_data_size * buffer_index;
+}
+
+/*
+ * Ask the callback which block it would like us to read next, with a small
+ * buffer in front to allow streaming_unget_block() to work.
+ */
+static BlockNumber
+streaming_read_get_block(StreamingRead *stream, void *per_buffer_data)
+{
+ BlockNumber result;
+
+ if (unlikely(stream->unget_blocknum != InvalidBlockNumber))
+ {
+ /*
+ * If we had to unget a block, now it is time to return that one
+ * again.
+ */
+ result = stream->unget_blocknum;
+ stream->unget_blocknum = InvalidBlockNumber;
+
+ /*
+ * The same per_buffer_data element must have been used, and still
+ * contains whatever data the callback wrote into it. So we just
+ * sanity-check that we were called with the value that
+ * streaming_unget_block() pushed back.
+ */
+ Assert(per_buffer_data == stream->unget_per_buffer_data);
+ }
+ else
+ {
+ /* Use the installed callback directly. */
+ result = stream->callback(stream,
+ stream->callback_private_data,
+ per_buffer_data);
+ }
+
+ return result;
+}
+
+/*
+ * In order to deal with short reads in StartReadBuffers(), we sometimes need
+ * to defer handling of a block until later. This *must* be called with the
+ * last value returned by streaming_get_block().
+ */
+static void
+streaming_read_unget_block(StreamingRead *stream, BlockNumber blocknum, void *per_buffer_data)
+{
+ Assert(stream->unget_blocknum == InvalidBlockNumber);
+ stream->unget_blocknum = blocknum;
+ stream->unget_per_buffer_data = per_buffer_data;
+}
+
+static void
+streaming_read_start_pending_read(StreamingRead *stream)
+{
+ bool need_wait;
+ int nblocks;
+ int16 io_index;
+ int16 overflow;
+ int flags;
+
+ /* This should only be called with a pending read. */
+ Assert(stream->pending_read_nblocks > 0);
+ Assert(stream->pending_read_nblocks <= buffer_io_size);
+
+ /* We had better not exceed the pin limit by starting this read. */
+ Assert(stream->pinned_buffers + stream->pending_read_nblocks <=
+ stream->max_pinned_buffers);
+
+ /* We had better not be overwriting an existing pinned buffer. */
+ if (stream->pinned_buffers > 0)
+ Assert(stream->next_buffer_index != stream->oldest_buffer_index);
+ else
+ Assert(stream->next_buffer_index == stream->oldest_buffer_index);
+
+ /*
+ * If advice hasn't been suppressed, and this system supports it, this
+ * isn't a strictly sequential pattern, then we'll issue advice.
+ */
+ if (stream->advice_enabled &&
+ stream->started &&
+ stream->pending_read_blocknum != stream->seq_blocknum)
+ flags = READ_BUFFERS_ISSUE_ADVICE;
+ else
+ flags = 0;
+
+ /* Suppress advice on the first call, because it's too late to benefit. */
+ if (!stream->started)
+ stream->started = true;
+
+ /* We say how many blocks we want to read, but may be smaller on return. */
+ nblocks = stream->pending_read_nblocks;
+ need_wait =
+ StartReadBuffers(stream->bmr,
+ &stream->buffers[stream->next_buffer_index],
+ stream->forknum,
+ stream->pending_read_blocknum,
+ &nblocks,
+ stream->strategy,
+ flags,
+ &stream->ios[stream->next_io_index]);
+ stream->pinned_buffers += nblocks;
+
+ /* Remember whether we need to wait before returning this buffer. */
+ if (!need_wait)
+ {
+ io_index = -1;
+
+ /* Look-ahead distance decays, no I/O necessary (behavior A). */
+ if (stream->distance > 1)
+ stream->distance--;
+ }
+ else
+ {
+ /*
+ * Remember to call WaitReadBuffers() before returning head buffer.
+ * Look-ahead distance will be adjusted after waiting.
+ */
+ io_index = stream->next_io_index;
+ if (++stream->next_io_index == stream->max_ios)
+ stream->next_io_index = 0;
+
+ Assert(stream->ios_in_progress < stream->max_ios);
+ stream->ios_in_progress++;
+ }
+
+ /* Set up the pointer to the I/O for the head buffer, if there is one. */
+ stream->buffer_io_indexes[stream->next_buffer_index] = io_index;
+
+ /*
+ * We gave a contiguous range of buffer space to StartReadBuffers(), but
+ * we want it to wrap around at max_pinned_buffers. Move values that
+ * overflowed into the extra space. At the same time, put -1 in the I/O
+ * slots for the rest of the buffers to indicate no I/O. They are covered
+ * by the head buffer's I/O, if there is one. We avoid a % operator.
+ */
+ overflow = (stream->next_buffer_index + nblocks) - stream->max_pinned_buffers;
+ if (overflow > 0)
+ {
+ memmove(&stream->buffers[0],
+ &stream->buffers[stream->max_pinned_buffers],
+ sizeof(stream->buffers[0]) * overflow);
+ for (int i = 0; i < overflow; ++i)
+ stream->buffer_io_indexes[i] = -1;
+ for (int i = 1; i < nblocks - overflow; ++i)
+ stream->buffer_io_indexes[stream->next_buffer_index + i] = -1;
+ }
+ else
+ {
+ for (int i = 1; i < nblocks; ++i)
+ stream->buffer_io_indexes[stream->next_buffer_index + i] = -1;
+ }
+
+ /*
+ * Remember where the next block would be after that, so we can detect
+ * sequential access next time and suppress advice.
+ */
+ stream->seq_blocknum = stream->pending_read_blocknum + nblocks;
+
+ /* Compute location of start of next read, without using % operator. */
+ stream->next_buffer_index += nblocks;
+ if (stream->next_buffer_index >= stream->max_pinned_buffers)
+ stream->next_buffer_index -= stream->max_pinned_buffers;
+ Assert(stream->next_buffer_index >= 0);
+ Assert(stream->next_buffer_index < stream->max_pinned_buffers);
+
+ /* Adjust the pending read to cover the remaining portion, if any. */
+ stream->pending_read_blocknum += nblocks;
+ stream->pending_read_nblocks -= nblocks;
+}
+
+static void
+streaming_read_look_ahead(StreamingRead *stream)
+{
+ while (!stream->finished &&
+ stream->ios_in_progress < stream->max_ios &&
+ stream->pinned_buffers + stream->pending_read_nblocks < stream->distance)
+ {
+ BlockNumber blocknum;
+ int16 buffer_index;
+ void *per_buffer_data;
+
+ if (stream->pending_read_nblocks == buffer_io_size)
+ {
+ streaming_read_start_pending_read(stream);
+ continue;
+ }
+
+ /*
+ * See which block the callback wants next in the stream. We need to
+ * compute the index of the Nth block of the pending read including
+ * wrap-around, but we don't want to use the expensive % operator.
+ */
+ buffer_index = stream->next_buffer_index + stream->pending_read_nblocks;
+ if (buffer_index > stream->max_pinned_buffers)
+ buffer_index -= stream->max_pinned_buffers;
+ per_buffer_data = get_per_buffer_data(stream, buffer_index);
+ blocknum = streaming_read_get_block(stream, per_buffer_data);
+ if (blocknum == InvalidBlockNumber)
+ {
+ stream->finished = true;
+ continue;
+ }
+
+ /* Can we merge it with the pending read? */
+ if (stream->pending_read_nblocks > 0 &&
+ stream->pending_read_blocknum + stream->pending_read_nblocks == blocknum)
+ {
+ stream->pending_read_nblocks++;
+ continue;
+ }
+
+ /* We have to start the pending read before we can build another. */
+ if (stream->pending_read_nblocks > 0)
+ {
+ streaming_read_start_pending_read(stream);
+ if (stream->ios_in_progress == stream->max_ios)
+ {
+ /* And we've hit the limit. Rewind, and stop here. */
+ streaming_read_unget_block(stream, blocknum, per_buffer_data);
+ return;
+ }
+ }
+
+ /* This is the start of a new pending read. */
+ stream->pending_read_blocknum = blocknum;
+ stream->pending_read_nblocks = 1;
+ }
+
+ /*
+ * Normally we don't start the pending read just because we've hit a
+ * limit, preferring to give it another chance to grow to a larger size
+ * once more buffers have been consumed. However, in cases where that
+ * can't possibly happen, we might as well start the read immediately.
+ */
+ if (((stream->pending_read_nblocks > 0 && stream->finished) ||
+ (stream->pending_read_nblocks == stream->distance)) &&
+ stream->ios_in_progress < stream->max_ios)
+ streaming_read_start_pending_read(stream);
+}
+
+/*
+ * Create a new streaming read object that can be used to perform the
+ * equivalent of a series of ReadBuffer() calls for one fork of one relation.
+ * Internally, it generates larger vectored reads where possible by looking
+ * ahead. The callback should return block numbers or InvalidBlockNumber to
+ * signal end-of-stream, and if per_buffer_data_size is non-zero, it may also
+ * write extra data for each block into the space provided to it. It will
+ * also receive callback_private_data for its own purposes.
+ */
+StreamingRead *
+streaming_read_buffer_begin(int flags,
+ BufferAccessStrategy strategy,
+ BufferManagerRelation bmr,
+ ForkNumber forknum,
+ StreamingReadBufferCB callback,
+ void *callback_private_data,
+ size_t per_buffer_data_size)
+{
+ StreamingRead *stream;
+ int16 max_ios;
+ uint32 max_pinned_buffers;
+ Oid tablespace_id;
+
+ /*
+ * Make sure our bmr's smgr and persistent are populated. The caller
+ * asserts that the storage manager will remain valid.
+ */
+ if (!bmr.smgr)
+ {
+ bmr.smgr = RelationGetSmgr(bmr.rel);
+ bmr.relpersistence = bmr.rel->rd_rel->relpersistence;
+ }
+
+ /*
+ * Decide how many assumed I/Os we will allow to run concurrently. That
+ * is, advice to the kernel to tell it that we will soon read. This
+ * number also affects how far we look ahead for opportunities to start
+ * more I/Os.
+ */
+ tablespace_id = bmr.smgr->smgr_rlocator.locator.spcOid;
+ if (!OidIsValid(MyDatabaseId) ||
+ (bmr.rel && IsCatalogRelation(bmr.rel)) ||
+ IsCatalogRelationOid(bmr.smgr->smgr_rlocator.locator.relNumber))
+ {
+ /*
+ * Avoid circularity while trying to look up tablespace settings or
+ * before spccache.c is ready.
+ */
+ max_ios = effective_io_concurrency;
+ }
+ else if (flags & STREAMING_READ_MAINTENANCE)
+ max_ios = get_tablespace_maintenance_io_concurrency(tablespace_id);
+ else
+ max_ios = get_tablespace_io_concurrency(tablespace_id);
+
+ /*
+ * Choose a maximum number of buffers we're prepared to pin. We try to
+ * pin fewer if we can, though. We clamp it to at least buffer_io_size so
+ * that we can have a chance to build up a full sized read, even when
+ * max_ios is zero.
+ */
+ max_pinned_buffers = Max(max_ios * 4, buffer_io_size);
+
+ /* Don't allow this backend to pin more than its share of buffers. */
+ if (SmgrIsTemp(bmr.smgr))
+ LimitAdditionalLocalPins(&max_pinned_buffers);
+ else
+ LimitAdditionalPins(&max_pinned_buffers);
+ Assert(max_pinned_buffers > 0);
+
+ stream = (StreamingRead *) palloc0(sizeof(StreamingRead));
+
+#ifdef USE_PREFETCH
+
+ /*
+ * This system supports prefetching advice. We can use it as long as
+ * direct I/O isn't enabled, the caller hasn't promised sequential access
+ * (overriding our detection heuristics), and max_ios hasn't been set to
+ * zero.
+ */
+ if ((io_direct_flags & IO_DIRECT_DATA) == 0 &&
+ (flags & STREAMING_READ_SEQUENTIAL) == 0 &&
+ max_ios > 0)
+ stream->advice_enabled = true;
+#endif
+
+ /*
+ * For now, max_ios = 0 is interpreted as max_ios = 1 with advice disabled
+ * above. If we had real asynchronous I/O we might need a slightly
+ * different definition.
+ */
+ if (max_ios == 0)
+ max_ios = 1;
+
+ stream->max_ios = max_ios;
+ stream->per_buffer_data_size = per_buffer_data_size;
+ stream->max_pinned_buffers = max_pinned_buffers;
+ stream->strategy = strategy;
+
+ stream->bmr = bmr;
+ stream->forknum = forknum;
+ stream->callback = callback;
+ stream->callback_private_data = callback_private_data;
+
+ stream->unget_blocknum = InvalidBlockNumber;
+
+ /*
+ * Skip the initial ramp-up phase if the caller says we're going to be
+ * reading the whole relation. This way we start out doing full-sized
+ * reads.
+ */
+ if (flags & STREAMING_READ_FULL)
+ stream->distance = stream->max_pinned_buffers;
+ else
+ stream->distance = 1;
+
+ /*
+ * Space for the buffers we pin. Though we never pin more than
+ * max_pinned_buffers, we want to be able to assume that all the buffers
+ * for a single read are contiguous (i.e. don't wrap around halfway
+ * through), so we let the final one run past that position temporarily by
+ * allocating an extra buffer_io_size - 1 elements.
+ */
+ stream->buffers = palloc((max_pinned_buffers + buffer_io_size - 1) *
+ sizeof(stream->buffers[0]));
+
+ /* Space for per-buffer data, if configured. */
+ if (per_buffer_data_size)
+ stream->per_buffer_data =
+ palloc(per_buffer_data_size * (max_pinned_buffers +
+ buffer_io_size - 1));
+
+ /* Space for the IOs that we might run. */
+ stream->buffer_io_indexes = palloc(max_pinned_buffers * sizeof(stream->buffer_io_indexes[0]));
+ stream->ios = palloc(max_ios * sizeof(ReadBuffersOperation));
+
+ return stream;
+}
+
+/*
+ * Pull one pinned buffer out of a stream created with
+ * streaming_read_buffer_begin(). Each call returns successive blocks in the
+ * order specified by the callback. If per_buffer_data_size was set to a
+ * non-zero size, *per_buffer_data receives a pointer to the extra per-buffer
+ * data that the callback had a chance to populate. When the stream runs out
+ * of data, InvalidBuffer is returned. The caller may decide to end the
+ * stream early at any time by calling streaming_read_end().
+ */
+Buffer
+streaming_read_buffer_next(StreamingRead *stream, void **per_buffer_data)
+{
+ Buffer buffer;
+ int16 io_index;
+ int16 oldest_buffer_index;
+
+ if (unlikely(stream->pinned_buffers == 0))
+ {
+ Assert(stream->oldest_buffer_index == stream->next_buffer_index);
+
+ if (stream->finished)
+ return InvalidBuffer;
+
+ /*
+ * The usual order of operations is that we look ahead at the bottom
+ * of this function after potentially finishing an I/O and making
+ * space for more, but we need a special case to prime the stream when
+ * we're getting started.
+ */
+ Assert(!stream->started);
+ streaming_read_look_ahead(stream);
+ if (stream->pinned_buffers == 0)
+ return InvalidBuffer;
+ }
+
+ /* Grab the oldest pinned buffer and associated per-buffer data. */
+ oldest_buffer_index = stream->oldest_buffer_index;
+ Assert(oldest_buffer_index >= 0 &&
+ oldest_buffer_index < stream->max_pinned_buffers);
+ buffer = stream->buffers[oldest_buffer_index];
+ if (per_buffer_data)
+ *per_buffer_data = get_per_buffer_data(stream, oldest_buffer_index);
+
+ Assert(BufferIsValid(buffer));
+
+ /* Do we have to wait for an associated I/O first? */
+ io_index = stream->buffer_io_indexes[oldest_buffer_index];
+ Assert(io_index >= -1 && io_index < stream->max_ios);
+ if (io_index >= 0)
+ {
+ int distance;
+
+ /* Sanity check that we still agree on the buffers. */
+ Assert(stream->ios[io_index].buffers == &stream->buffers[oldest_buffer_index]);
+
+ WaitReadBuffers(&stream->ios[io_index]);
+
+ Assert(stream->ios_in_progress > 0);
+ stream->ios_in_progress--;
+
+ if (stream->ios[io_index].flags & READ_BUFFERS_ISSUE_ADVICE)
+ {
+ /* Distance ramps up fast (behavior C). */
+ distance = stream->distance * 2;
+ distance = Min(distance, stream->max_pinned_buffers);
+ stream->distance = distance;
+ }
+ else
+ {
+ /* No advice; move towards full I/O size (behavior B). */
+ if (stream->distance > buffer_io_size)
+ {
+ stream->distance--;
+ }
+ else
+ {
+ distance = stream->distance * 2;
+ distance = Min(distance, buffer_io_size);
+ distance = Min(distance, stream->max_pinned_buffers);
+ stream->distance = distance;
+ }
+ }
+ }
+
+ /* Advance the oldest buffer, but clobber it first for debugging. */
+#ifdef USE_ASSERT_CHECKING
+ stream->buffers[oldest_buffer_index] = InvalidBuffer;
+ stream->buffer_io_indexes[oldest_buffer_index] = -1;
+ if (stream->per_buffer_data)
+ memset(get_per_buffer_data(stream, oldest_buffer_index),
+ 0xff,
+ stream->per_buffer_data_size);
+#endif
+ if (++stream->oldest_buffer_index == stream->max_pinned_buffers)
+ stream->oldest_buffer_index = 0;
+
+ /* We are transferring ownership of the pin to the caller. */
+ Assert(stream->pinned_buffers > 0);
+ stream->pinned_buffers--;
+
+ /*
+ * When distance is minimal, we finish up with no queued buffers. As a
+ * micro-optimization, we can then reset our circular queues, so that
+ * all-cached streams re-use the same elements instead of rotating through
+ * memory.
+ */
+ if (stream->pinned_buffers == 0)
+ {
+ Assert(stream->oldest_buffer_index == stream->next_buffer_index);
+ stream->oldest_buffer_index = 0;
+ stream->next_buffer_index = 0;
+ stream->next_io_index = 0;
+ }
+
+ /* Prepare for the next call. */
+ streaming_read_look_ahead(stream);
+
+ return buffer;
+}
+
+/*
+ * Finish streaming blocks and release all resources.
+ */
+void
+streaming_read_buffer_end(StreamingRead *stream)
+{
+ Buffer buffer;
+
+ /* Stop looking ahead. */
+ stream->finished = true;
+
+ /* Unpin anything that wasn't consumed. */
+ while ((buffer = streaming_read_buffer_next(stream, NULL)) != InvalidBuffer)
+ ReleaseBuffer(buffer);
+
+ Assert(stream->pinned_buffers == 0);
+ Assert(stream->ios_in_progress == 0);
+
+ /* Release memory. */
+ pfree(stream->buffers);
+ if (stream->per_buffer_data)
+ pfree(stream->per_buffer_data);
+ pfree(stream->ios);
+
+ pfree(stream);
+}
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index f0f8d4259c5..b5347678726 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -19,6 +19,11 @@
* and pin it so that no one can destroy it while this process
* is using it.
*
+ * StartReadBuffers() -- as above, but for multiple contiguous blocks in
+ * two steps.
+ *
+ * WaitReadBuffers() -- second step of StartReadBuffers().
+ *
* ReleaseBuffer() -- unpin a buffer
*
* MarkBufferDirty() -- mark a pinned buffer's contents as "dirty".
@@ -160,6 +165,12 @@ int checkpoint_flush_after = DEFAULT_CHECKPOINT_FLUSH_AFTER;
int bgwriter_flush_after = DEFAULT_BGWRITER_FLUSH_AFTER;
int backend_flush_after = DEFAULT_BACKEND_FLUSH_AFTER;
+/*
+ * How many buffers should be coalesced into single I/O operations where
+ * possible.
+ */
+int buffer_io_size = DEFAULT_BUFFER_IO_SIZE;
+
/* local state for LockBufferForCleanup */
static BufferDesc *PinCountWaitBuf = NULL;
@@ -471,10 +482,9 @@ ForgetPrivateRefCountEntry(PrivateRefCountEntry *ref)
)
-static Buffer ReadBuffer_common(SMgrRelation smgr, char relpersistence,
+static Buffer ReadBuffer_common(BufferManagerRelation bmr,
ForkNumber forkNum, BlockNumber blockNum,
- ReadBufferMode mode, BufferAccessStrategy strategy,
- bool *hit);
+ ReadBufferMode mode, BufferAccessStrategy strategy);
static BlockNumber ExtendBufferedRelCommon(BufferManagerRelation bmr,
ForkNumber fork,
BufferAccessStrategy strategy,
@@ -500,7 +510,7 @@ static uint32 WaitBufHdrUnlocked(BufferDesc *buf);
static int SyncOneBuffer(int buf_id, bool skip_recently_used,
WritebackContext *wb_context);
static void WaitIO(BufferDesc *buf);
-static bool StartBufferIO(BufferDesc *buf, bool forInput);
+static bool StartBufferIO(BufferDesc *buf, bool forInput, bool nowait);
static void TerminateBufferIO(BufferDesc *buf, bool clear_dirty,
uint32 set_flag_bits, bool forget_owner);
static void AbortBufferIO(Buffer buffer);
@@ -781,7 +791,6 @@ Buffer
ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum,
ReadBufferMode mode, BufferAccessStrategy strategy)
{
- bool hit;
Buffer buf;
/*
@@ -794,15 +803,9 @@ ReadBufferExtended(Relation reln, ForkNumber forkNum, BlockNumber blockNum,
(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
errmsg("cannot access temporary tables of other sessions")));
- /*
- * Read the buffer, and update pgstat counters to reflect a cache hit or
- * miss.
- */
- pgstat_count_buffer_read(reln);
- buf = ReadBuffer_common(RelationGetSmgr(reln), reln->rd_rel->relpersistence,
- forkNum, blockNum, mode, strategy, &hit);
- if (hit)
- pgstat_count_buffer_hit(reln);
+ buf = ReadBuffer_common(BMR_REL(reln),
+ forkNum, blockNum, mode, strategy);
+
return buf;
}
@@ -822,13 +825,12 @@ ReadBufferWithoutRelcache(RelFileLocator rlocator, ForkNumber forkNum,
BlockNumber blockNum, ReadBufferMode mode,
BufferAccessStrategy strategy, bool permanent)
{
- bool hit;
-
SMgrRelation smgr = smgropen(rlocator, INVALID_PROC_NUMBER);
- return ReadBuffer_common(smgr, permanent ? RELPERSISTENCE_PERMANENT :
- RELPERSISTENCE_UNLOGGED, forkNum, blockNum,
- mode, strategy, &hit);
+ return ReadBuffer_common(BMR_SMGR(smgr, permanent ? RELPERSISTENCE_PERMANENT :
+ RELPERSISTENCE_UNLOGGED),
+ forkNum, blockNum,
+ mode, strategy);
}
/*
@@ -994,35 +996,66 @@ ExtendBufferedRelTo(BufferManagerRelation bmr,
*/
if (buffer == InvalidBuffer)
{
- bool hit;
-
Assert(extended_by == 0);
- buffer = ReadBuffer_common(bmr.smgr, bmr.relpersistence,
- fork, extend_to - 1, mode, strategy,
- &hit);
+ buffer = ReadBuffer_common(bmr, fork, extend_to - 1, mode, strategy);
}
return buffer;
}
/*
- * ReadBuffer_common -- common logic for all ReadBuffer variants
- *
- * *hit is set to true if the request was satisfied from shared buffer cache.
+ * Zero a buffer and lock it, as part of the implementation of
+ * RBM_ZERO_AND_LOCK or RBM_ZERO_AND_CLEANUP_LOCK. The buffer must be already
+ * pinned. It does not have to be valid, but it is valid and locked on
+ * return.
*/
-static Buffer
-ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
- BlockNumber blockNum, ReadBufferMode mode,
- BufferAccessStrategy strategy, bool *hit)
+static void
+ZeroBuffer(Buffer buffer, ReadBufferMode mode)
{
BufferDesc *bufHdr;
- Block bufBlock;
- bool found;
- IOContext io_context;
- IOObject io_object;
- bool isLocalBuf = SmgrIsTemp(smgr);
+ uint32 buf_state;
- *hit = false;
+ Assert(mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK);
+
+ if (BufferIsLocal(buffer))
+ bufHdr = GetLocalBufferDescriptor(-buffer - 1);
+ else
+ {
+ bufHdr = GetBufferDescriptor(buffer - 1);
+ if (mode == RBM_ZERO_AND_LOCK)
+ LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
+ else
+ LockBufferForCleanup(buffer);
+ }
+
+ memset(BufferGetPage(buffer), 0, BLCKSZ);
+
+ if (BufferIsLocal(buffer))
+ {
+ buf_state = pg_atomic_read_u32(&bufHdr->state);
+ buf_state |= BM_VALID;
+ pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
+ }
+ else
+ {
+ buf_state = LockBufHdr(bufHdr);
+ buf_state |= BM_VALID;
+ UnlockBufHdr(bufHdr, buf_state);
+ }
+}
+
+/*
+ * ReadBuffer_common -- common logic for all ReadBuffer variants
+ */
+static Buffer
+ReadBuffer_common(BufferManagerRelation bmr, ForkNumber forkNum,
+ BlockNumber blockNum, ReadBufferMode mode,
+ BufferAccessStrategy strategy)
+{
+ ReadBuffersOperation operation;
+ Buffer buffer;
+ int nblocks;
+ int flags;
/*
* Backward compatibility path, most code should use ExtendBufferedRel()
@@ -1041,181 +1074,413 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
flags |= EB_LOCK_FIRST;
- return ExtendBufferedRel(BMR_SMGR(smgr, relpersistence),
- forkNum, strategy, flags);
+ return ExtendBufferedRel(bmr, forkNum, strategy, flags);
}
- TRACE_POSTGRESQL_BUFFER_READ_START(forkNum, blockNum,
- smgr->smgr_rlocator.locator.spcOid,
- smgr->smgr_rlocator.locator.dbOid,
- smgr->smgr_rlocator.locator.relNumber,
- smgr->smgr_rlocator.backend);
+ nblocks = 1;
+ if (mode == RBM_ZERO_ON_ERROR)
+ flags = READ_BUFFERS_ZERO_ON_ERROR;
+ else
+ flags = 0;
+ if (StartReadBuffers(bmr,
+ &buffer,
+ forkNum,
+ blockNum,
+ &nblocks,
+ strategy,
+ flags,
+ &operation))
+ WaitReadBuffers(&operation);
+ Assert(nblocks == 1); /* single block can't be short */
+ if (mode == RBM_ZERO_AND_CLEANUP_LOCK || mode == RBM_ZERO_AND_LOCK)
+ ZeroBuffer(buffer, mode);
+
+ return buffer;
+}
+
+/*
+ * Pin a buffer for a given block. *foundPtr is set to true if the block was
+ * already present, or false if more work is required to either read it in or
+ * zero it.
+ */
+static inline Buffer
+PinBufferForBlock(BufferManagerRelation bmr,
+ ForkNumber forkNum,
+ BlockNumber blockNum,
+ BufferAccessStrategy strategy,
+ bool *foundPtr)
+{
+ BufferDesc *bufHdr;
+ bool isLocalBuf;
+ IOContext io_context;
+ IOObject io_object;
+
+ Assert(blockNum != P_NEW);
+
+ Assert(bmr.smgr);
+
+ isLocalBuf = SmgrIsTemp(bmr.smgr);
if (isLocalBuf)
{
- /*
- * We do not use a BufferAccessStrategy for I/O of temporary tables.
- * However, in some cases, the "strategy" may not be NULL, so we can't
- * rely on IOContextForStrategy() to set the right IOContext for us.
- * This may happen in cases like CREATE TEMPORARY TABLE AS...
- */
io_context = IOCONTEXT_NORMAL;
io_object = IOOBJECT_TEMP_RELATION;
- bufHdr = LocalBufferAlloc(smgr, forkNum, blockNum, &found);
- if (found)
- pgBufferUsage.local_blks_hit++;
- else if (mode == RBM_NORMAL || mode == RBM_NORMAL_NO_LOG ||
- mode == RBM_ZERO_ON_ERROR)
- pgBufferUsage.local_blks_read++;
}
else
{
- /*
- * lookup the buffer. IO_IN_PROGRESS is set if the requested block is
- * not currently in memory.
- */
io_context = IOContextForStrategy(strategy);
io_object = IOOBJECT_RELATION;
- bufHdr = BufferAlloc(smgr, relpersistence, forkNum, blockNum,
- strategy, &found, io_context);
- if (found)
- pgBufferUsage.shared_blks_hit++;
- else if (mode == RBM_NORMAL || mode == RBM_NORMAL_NO_LOG ||
- mode == RBM_ZERO_ON_ERROR)
- pgBufferUsage.shared_blks_read++;
}
- /* At this point we do NOT hold any locks. */
+ TRACE_POSTGRESQL_BUFFER_READ_START(forkNum, blockNum,
+ bmr.smgr->smgr_rlocator.locator.spcOid,
+ bmr.smgr->smgr_rlocator.locator.dbOid,
+ bmr.smgr->smgr_rlocator.locator.relNumber,
+ bmr.smgr->smgr_rlocator.backend);
- /* if it was already in the buffer pool, we're done */
- if (found)
+ if (isLocalBuf)
+ {
+ bufHdr = LocalBufferAlloc(bmr.smgr, forkNum, blockNum, foundPtr);
+ if (*foundPtr)
+ pgBufferUsage.local_blks_hit++;
+ }
+ else
+ {
+ bufHdr = BufferAlloc(bmr.smgr, bmr.relpersistence, forkNum, blockNum,
+ strategy, foundPtr, io_context);
+ if (*foundPtr)
+ pgBufferUsage.shared_blks_hit++;
+ }
+ if (bmr.rel)
+ {
+ /*
+ * While pgBufferUsage's "read" counter isn't bumped unless we reach
+ * WaitReadBuffers() (so, not for hits, and not for buffers that are
+ * zeroed instead), the per-relation stats always count them.
+ */
+ pgstat_count_buffer_read(bmr.rel);
+ if (*foundPtr)
+ pgstat_count_buffer_hit(bmr.rel);
+ }
+ if (*foundPtr)
{
- /* Just need to update stats before we exit */
- *hit = true;
VacuumPageHit++;
pgstat_count_io_op(io_object, io_context, IOOP_HIT);
-
if (VacuumCostActive)
VacuumCostBalance += VacuumCostPageHit;
TRACE_POSTGRESQL_BUFFER_READ_DONE(forkNum, blockNum,
- smgr->smgr_rlocator.locator.spcOid,
- smgr->smgr_rlocator.locator.dbOid,
- smgr->smgr_rlocator.locator.relNumber,
- smgr->smgr_rlocator.backend,
- found);
-
- /*
- * In RBM_ZERO_AND_LOCK mode the caller expects the page to be locked
- * on return.
- */
- if (!isLocalBuf)
- {
- if (mode == RBM_ZERO_AND_LOCK)
- LWLockAcquire(BufferDescriptorGetContentLock(bufHdr),
- LW_EXCLUSIVE);
- else if (mode == RBM_ZERO_AND_CLEANUP_LOCK)
- LockBufferForCleanup(BufferDescriptorGetBuffer(bufHdr));
- }
-
- return BufferDescriptorGetBuffer(bufHdr);
+ bmr.smgr->smgr_rlocator.locator.spcOid,
+ bmr.smgr->smgr_rlocator.locator.dbOid,
+ bmr.smgr->smgr_rlocator.locator.relNumber,
+ bmr.smgr->smgr_rlocator.backend,
+ true);
}
- /*
- * if we have gotten to this point, we have allocated a buffer for the
- * page but its contents are not yet valid. IO_IN_PROGRESS is set for it,
- * if it's a shared buffer.
- */
- Assert(!(pg_atomic_read_u32(&bufHdr->state) & BM_VALID)); /* spinlock not needed */
-
- bufBlock = isLocalBuf ? LocalBufHdrGetBlock(bufHdr) : BufHdrGetBlock(bufHdr);
-
- /*
- * Read in the page, unless the caller intends to overwrite it and just
- * wants us to allocate a buffer.
- */
- if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
- MemSet((char *) bufBlock, 0, BLCKSZ);
- else
- {
- instr_time io_start = pgstat_prepare_io_time(track_io_timing);
-
- smgrread(smgr, forkNum, blockNum, bufBlock);
-
- pgstat_count_io_op_time(io_object, io_context,
- IOOP_READ, io_start, 1);
-
- /* check for garbage data */
- if (!PageIsVerifiedExtended((Page) bufBlock, blockNum,
- PIV_LOG_WARNING | PIV_REPORT_STAT))
- {
- if (mode == RBM_ZERO_ON_ERROR || zero_damaged_pages)
- {
- ereport(WARNING,
- (errcode(ERRCODE_DATA_CORRUPTED),
- errmsg("invalid page in block %u of relation %s; zeroing out page",
- blockNum,
- relpath(smgr->smgr_rlocator, forkNum))));
- MemSet((char *) bufBlock, 0, BLCKSZ);
- }
- else
- ereport(ERROR,
- (errcode(ERRCODE_DATA_CORRUPTED),
- errmsg("invalid page in block %u of relation %s",
- blockNum,
- relpath(smgr->smgr_rlocator, forkNum))));
- }
- }
-
- /*
- * In RBM_ZERO_AND_LOCK / RBM_ZERO_AND_CLEANUP_LOCK mode, grab the buffer
- * content lock before marking the page as valid, to make sure that no
- * other backend sees the zeroed page before the caller has had a chance
- * to initialize it.
- *
- * Since no-one else can be looking at the page contents yet, there is no
- * difference between an exclusive lock and a cleanup-strength lock. (Note
- * that we cannot use LockBuffer() or LockBufferForCleanup() here, because
- * they assert that the buffer is already valid.)
- */
- if ((mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK) &&
- !isLocalBuf)
- {
- LWLockAcquire(BufferDescriptorGetContentLock(bufHdr), LW_EXCLUSIVE);
- }
-
- if (isLocalBuf)
- {
- /* Only need to adjust flags */
- uint32 buf_state = pg_atomic_read_u32(&bufHdr->state);
-
- buf_state |= BM_VALID;
- pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
- }
- else
- {
- /* Set BM_VALID, terminate IO, and wake up any waiters */
- TerminateBufferIO(bufHdr, false, BM_VALID, true);
- }
-
- VacuumPageMiss++;
- if (VacuumCostActive)
- VacuumCostBalance += VacuumCostPageMiss;
-
- TRACE_POSTGRESQL_BUFFER_READ_DONE(forkNum, blockNum,
- smgr->smgr_rlocator.locator.spcOid,
- smgr->smgr_rlocator.locator.dbOid,
- smgr->smgr_rlocator.locator.relNumber,
- smgr->smgr_rlocator.backend,
- found);
-
return BufferDescriptorGetBuffer(bufHdr);
}
/*
- * BufferAlloc -- subroutine for ReadBuffer. Handles lookup of a shared
- * buffer. If no buffer exists already, selects a replacement
- * victim and evicts the old page, but does NOT read in new page.
+ * Begin reading a range of blocks beginning at blockNum and extending for
+ * *nblocks. On return, up to *nblocks pinned buffers holding those blocks
+ * are written into the buffers array, and *nblocks is updated to contain the
+ * actual number, which may be fewer than requested.
+ *
+ * If false is returned, no I/O is necessary and WaitReadBuffers() is not
+ * necessary. If true is returned, one I/O has been started, and
+ * WaitReadBuffers() must be called with the same operation object before the
+ * buffers are accessed. Along with the operation object, the caller-supplied
+ * array of buffers must remain valid until WaitReadBuffers() is called.
+ *
+ * Currently the I/O is only started with optional operating system advice,
+ * and the real I/O happens in WaitReadBuffers(). In future work, true I/O
+ * could be initiated here.
+ */
+bool
+StartReadBuffers(BufferManagerRelation bmr,
+ Buffer *buffers,
+ ForkNumber forkNum,
+ BlockNumber blockNum,
+ int *nblocks,
+ BufferAccessStrategy strategy,
+ int flags,
+ ReadBuffersOperation *operation)
+{
+ int actual_nblocks = *nblocks;
+ int io_buffers_len = 0;
+
+ Assert(*nblocks > 0);
+ Assert(*nblocks <= MAX_BUFFER_IO_SIZE);
+
+ if (bmr.rel)
+ {
+ bmr.smgr = RelationGetSmgr(bmr.rel);
+ bmr.relpersistence = bmr.rel->rd_rel->relpersistence;
+ }
+
+ for (int i = 0; i < actual_nblocks; ++i)
+ {
+ bool found;
+
+ buffers[i] = PinBufferForBlock(bmr,
+ forkNum,
+ blockNum + i,
+ strategy,
+ &found);
+
+ if (found)
+ {
+ /*
+ * Terminate the read as soon as we get a hit. It could be a
+ * single buffer hit, or it could be a hit that follows a readable
+ * range. We don't want to create more than one readable range,
+ * so we stop here.
+ */
+ actual_nblocks = operation->nblocks = *nblocks = i + 1;
+ break;
+ }
+ else
+ {
+ /* Extend the readable range to cover this block. */
+ io_buffers_len++;
+ }
+ }
+
+ if (io_buffers_len > 0)
+ {
+ /* Populate extra information needed for I/O. */
+ operation->io_buffers_len = io_buffers_len;
+ operation->blocknum = blockNum;
+ operation->buffers = buffers;
+ operation->nblocks = actual_nblocks;
+ operation->bmr = bmr;
+ operation->forknum = forkNum;
+ operation->strategy = strategy;
+ operation->flags = flags;
+
+ if (flags & READ_BUFFERS_ISSUE_ADVICE)
+ {
+ /*
+ * In theory we should only do this if PinBufferForBlock() had to
+ * allocate new buffers above. That way, if two calls to
+ * StartReadBuffers() were made for the same blocks before
+ * WaitReadBuffers(), only the first would issue the advice.
+ * That'd be a better simulation of true asynchronous I/O, which
+ * would only start the I/O once, but isn't done here for
+ * simplicity. Note also that the following call might actually
+ * issue two advice calls if we cross a segment boundary; in a
+ * true asynchronous version we might choose to process only one
+ * real I/O at a time in that case.
+ */
+ smgrprefetch(bmr.smgr, forkNum, blockNum, operation->io_buffers_len);
+ }
+
+ /* Indicate that WaitReadBuffers() should be called. */
+ return true;
+ }
+ else
+ {
+ return false;
+ }
+}
+
+static inline bool
+WaitReadBuffersCanStartIO(Buffer buffer, bool nowait)
+{
+ if (BufferIsLocal(buffer))
+ {
+ BufferDesc *bufHdr = GetLocalBufferDescriptor(-buffer - 1);
+
+ return (pg_atomic_read_u32(&bufHdr->state) & BM_VALID) == 0;
+ }
+ else
+ return StartBufferIO(GetBufferDescriptor(buffer - 1), true, nowait);
+}
+
+void
+WaitReadBuffers(ReadBuffersOperation *operation)
+{
+ BufferManagerRelation bmr;
+ Buffer *buffers;
+ int nblocks;
+ BlockNumber blocknum;
+ ForkNumber forknum;
+ bool isLocalBuf;
+ IOContext io_context;
+ IOObject io_object;
+
+ /*
+ * Currently operations are only allowed to include a read of some range,
+ * with an optional extra buffer that is already pinned at the end. So
+ * nblocks can be at most one more than io_buffers_len.
+ */
+ Assert((operation->nblocks == operation->io_buffers_len) ||
+ (operation->nblocks == operation->io_buffers_len + 1));
+
+ /* Find the range of the physical read we need to perform. */
+ nblocks = operation->io_buffers_len;
+ if (nblocks == 0)
+ return; /* nothing to do */
+
+ buffers = &operation->buffers[0];
+ blocknum = operation->blocknum;
+ forknum = operation->forknum;
+ bmr = operation->bmr;
+
+ isLocalBuf = SmgrIsTemp(bmr.smgr);
+ if (isLocalBuf)
+ {
+ io_context = IOCONTEXT_NORMAL;
+ io_object = IOOBJECT_TEMP_RELATION;
+ }
+ else
+ {
+ io_context = IOContextForStrategy(operation->strategy);
+ io_object = IOOBJECT_RELATION;
+ }
+
+ /*
+ * We count all these blocks as read by this backend. This is traditional
+ * behavior, but might turn out to be not true if we find that someone
+ * else has beaten us and completed the read of some of these blocks. In
+ * that case the system globally double-counts, but we traditionally don't
+ * count this as a "hit", and we don't have a separate counter for "miss,
+ * but another backend completed the read".
+ */
+ if (isLocalBuf)
+ pgBufferUsage.local_blks_read += nblocks;
+ else
+ pgBufferUsage.shared_blks_read += nblocks;
+
+ for (int i = 0; i < nblocks; ++i)
+ {
+ int io_buffers_len;
+ Buffer io_buffers[MAX_BUFFER_IO_SIZE];
+ void *io_pages[MAX_BUFFER_IO_SIZE];
+ instr_time io_start;
+ BlockNumber io_first_block;
+
+ /*
+ * Skip this block if someone else has already completed it. If an
+ * I/O is already in progress in another backend, this will wait for
+ * the outcome: either done, or something went wrong and we will
+ * retry.
+ */
+ if (!WaitReadBuffersCanStartIO(buffers[i], false))
+ {
+ /*
+ * Report this as a 'hit' for this backend, even though it must
+ * have started out as a miss in PinBufferForBlock().
+ */
+ TRACE_POSTGRESQL_BUFFER_READ_DONE(forknum, blocknum + i,
+ bmr.smgr->smgr_rlocator.locator.spcOid,
+ bmr.smgr->smgr_rlocator.locator.dbOid,
+ bmr.smgr->smgr_rlocator.locator.relNumber,
+ bmr.smgr->smgr_rlocator.backend,
+ true);
+ continue;
+ }
+
+ /* We found a buffer that we need to read in. */
+ io_buffers[0] = buffers[i];
+ io_pages[0] = BufferGetBlock(buffers[i]);
+ io_first_block = blocknum + i;
+ io_buffers_len = 1;
+
+ /*
+ * How many neighboring-on-disk blocks can we can scatter-read into
+ * other buffers at the same time? In this case we don't wait if we
+ * see an I/O already in progress. We already hold BM_IO_IN_PROGRESS
+ * for the head block, so we should get on with that I/O as soon as
+ * possible. We'll come back to this block again, above.
+ */
+ while ((i + 1) < nblocks &&
+ WaitReadBuffersCanStartIO(buffers[i + 1], true))
+ {
+ /* Must be consecutive block numbers. */
+ Assert(BufferGetBlockNumber(buffers[i + 1]) ==
+ BufferGetBlockNumber(buffers[i]) + 1);
+
+ io_buffers[io_buffers_len] = buffers[++i];
+ io_pages[io_buffers_len++] = BufferGetBlock(buffers[i]);
+ }
+
+ io_start = pgstat_prepare_io_time(track_io_timing);
+ smgrreadv(bmr.smgr, forknum, io_first_block, io_pages, io_buffers_len);
+ pgstat_count_io_op_time(io_object, io_context, IOOP_READ, io_start,
+ io_buffers_len);
+
+ /* Verify each block we read, and terminate the I/O. */
+ for (int j = 0; j < io_buffers_len; ++j)
+ {
+ BufferDesc *bufHdr;
+ Block bufBlock;
+
+ if (isLocalBuf)
+ {
+ bufHdr = GetLocalBufferDescriptor(-io_buffers[j] - 1);
+ bufBlock = LocalBufHdrGetBlock(bufHdr);
+ }
+ else
+ {
+ bufHdr = GetBufferDescriptor(io_buffers[j] - 1);
+ bufBlock = BufHdrGetBlock(bufHdr);
+ }
+
+ /* check for garbage data */
+ if (!PageIsVerifiedExtended((Page) bufBlock, io_first_block + j,
+ PIV_LOG_WARNING | PIV_REPORT_STAT))
+ {
+ if ((operation->flags & READ_BUFFERS_ZERO_ON_ERROR) || zero_damaged_pages)
+ {
+ ereport(WARNING,
+ (errcode(ERRCODE_DATA_CORRUPTED),
+ errmsg("invalid page in block %u of relation %s; zeroing out page",
+ io_first_block + j,
+ relpath(bmr.smgr->smgr_rlocator, forknum))));
+ memset(bufBlock, 0, BLCKSZ);
+ }
+ else
+ ereport(ERROR,
+ (errcode(ERRCODE_DATA_CORRUPTED),
+ errmsg("invalid page in block %u of relation %s",
+ io_first_block + j,
+ relpath(bmr.smgr->smgr_rlocator, forknum))));
+ }
+
+ /* Terminate I/O and set BM_VALID. */
+ if (isLocalBuf)
+ {
+ uint32 buf_state = pg_atomic_read_u32(&bufHdr->state);
+
+ buf_state |= BM_VALID;
+ pg_atomic_unlocked_write_u32(&bufHdr->state, buf_state);
+ }
+ else
+ {
+ /* Set BM_VALID, terminate IO, and wake up any waiters */
+ TerminateBufferIO(bufHdr, false, BM_VALID, true);
+ }
+
+ /* Report I/Os as completing individually. */
+ TRACE_POSTGRESQL_BUFFER_READ_DONE(forknum, io_first_block + j,
+ bmr.smgr->smgr_rlocator.locator.spcOid,
+ bmr.smgr->smgr_rlocator.locator.dbOid,
+ bmr.smgr->smgr_rlocator.locator.relNumber,
+ bmr.smgr->smgr_rlocator.backend,
+ false);
+ }
+
+ VacuumPageMiss += io_buffers_len;
+ if (VacuumCostActive)
+ VacuumCostBalance += VacuumCostPageMiss * io_buffers_len;
+ }
+}
+
+/*
+ * BufferAlloc -- subroutine for PinBufferForBlock. Handles lookup of a shared
+ * buffer. If no buffer exists already, selects a replacement victim and
+ * evicts the old page, but does NOT read in new page.
*
* "strategy" can be a buffer replacement strategy object, or NULL for
* the default strategy. The selected buffer's usage_count is advanced when
@@ -1223,11 +1488,7 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
*
* The returned buffer is pinned and is already marked as holding the
* desired page. If it already did have the desired page, *foundPtr is
- * set true. Otherwise, *foundPtr is set false and the buffer is marked
- * as IO_IN_PROGRESS; ReadBuffer will now need to do I/O to fill it.
- *
- * *foundPtr is actually redundant with the buffer's BM_VALID flag, but
- * we keep it for simplicity in ReadBuffer.
+ * set true. Otherwise, *foundPtr is set false.
*
* io_context is passed as an output parameter to avoid calling
* IOContextForStrategy() when there is a shared buffers hit and no IO
@@ -1286,19 +1547,10 @@ BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
{
/*
* We can only get here if (a) someone else is still reading in
- * the page, or (b) a previous read attempt failed. We have to
- * wait for any active read attempt to finish, and then set up our
- * own read attempt if the page is still not BM_VALID.
- * StartBufferIO does it all.
+ * the page, (b) a previous read attempt failed, or (c) someone
+ * called StartReadBuffers() but not yet WaitReadBuffers().
*/
- if (StartBufferIO(buf, true))
- {
- /*
- * If we get here, previous attempts to read the buffer must
- * have failed ... but we shall bravely try again.
- */
- *foundPtr = false;
- }
+ *foundPtr = false;
}
return buf;
@@ -1363,19 +1615,10 @@ BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
{
/*
* We can only get here if (a) someone else is still reading in
- * the page, or (b) a previous read attempt failed. We have to
- * wait for any active read attempt to finish, and then set up our
- * own read attempt if the page is still not BM_VALID.
- * StartBufferIO does it all.
+ * the page, (b) a previous read attempt failed, or (c) someone
+ * called StartReadBuffers() but not yet WaitReadBuffers().
*/
- if (StartBufferIO(existing_buf_hdr, true))
- {
- /*
- * If we get here, previous attempts to read the buffer must
- * have failed ... but we shall bravely try again.
- */
- *foundPtr = false;
- }
+ *foundPtr = false;
}
return existing_buf_hdr;
@@ -1407,15 +1650,9 @@ BufferAlloc(SMgrRelation smgr, char relpersistence, ForkNumber forkNum,
LWLockRelease(newPartitionLock);
/*
- * Buffer contents are currently invalid. Try to obtain the right to
- * start I/O. If StartBufferIO returns false, then someone else managed
- * to read it before we did, so there's nothing left for BufferAlloc() to
- * do.
+ * Buffer contents are currently invalid.
*/
- if (StartBufferIO(victim_buf_hdr, true))
- *foundPtr = false;
- else
- *foundPtr = true;
+ *foundPtr = false;
return victim_buf_hdr;
}
@@ -1769,7 +2006,7 @@ again:
* pessimistic, but outside of toy-sized shared_buffers it should allow
* sufficient pins.
*/
-static void
+void
LimitAdditionalPins(uint32 *additional_pins)
{
uint32 max_backends;
@@ -2034,7 +2271,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
buf_state &= ~BM_VALID;
UnlockBufHdr(existing_hdr, buf_state);
- } while (!StartBufferIO(existing_hdr, true));
+ } while (!StartBufferIO(existing_hdr, true, false));
}
else
{
@@ -2057,7 +2294,7 @@ ExtendBufferedRelShared(BufferManagerRelation bmr,
LWLockRelease(partition_lock);
/* XXX: could combine the locked operations in it with the above */
- StartBufferIO(victim_buf_hdr, true);
+ StartBufferIO(victim_buf_hdr, true, false);
}
}
@@ -2372,7 +2609,12 @@ PinBuffer(BufferDesc *buf, BufferAccessStrategy strategy)
else
{
/*
- * If we previously pinned the buffer, it must surely be valid.
+ * If we previously pinned the buffer, it is likely to be valid, but
+ * it may not be if StartReadBuffers() was called and
+ * WaitReadBuffers() hasn't been called yet. We'll check by loading
+ * the flags without locking. This is racy, but it's OK to return
+ * false spuriously: when WaitReadBuffers() calls StartBufferIO(),
+ * it'll see that it's now valid.
*
* Note: We deliberately avoid a Valgrind client request here.
* Individual access methods can optionally superimpose buffer page
@@ -2381,7 +2623,7 @@ PinBuffer(BufferDesc *buf, BufferAccessStrategy strategy)
* that the buffer page is legitimately non-accessible here. We
* cannot meddle with that.
*/
- result = true;
+ result = (pg_atomic_read_u32(&buf->state) & BM_VALID) != 0;
}
ref->refcount++;
@@ -3449,7 +3691,7 @@ FlushBuffer(BufferDesc *buf, SMgrRelation reln, IOObject io_object,
* someone else flushed the buffer before we could, so we need not do
* anything.
*/
- if (!StartBufferIO(buf, false))
+ if (!StartBufferIO(buf, false, false))
return;
/* Setup error traceback support for ereport() */
@@ -5184,9 +5426,15 @@ WaitIO(BufferDesc *buf)
*
* Returns true if we successfully marked the buffer as I/O busy,
* false if someone else already did the work.
+ *
+ * If nowait is true, then we don't wait for an I/O to be finished by another
+ * backend. In that case, false indicates either that the I/O was already
+ * finished, or is still in progress. This is useful for callers that want to
+ * find out if they can perform the I/O as part of a larger operation, without
+ * waiting for the answer or distinguishing the reasons why not.
*/
static bool
-StartBufferIO(BufferDesc *buf, bool forInput)
+StartBufferIO(BufferDesc *buf, bool forInput, bool nowait)
{
uint32 buf_state;
@@ -5199,6 +5447,8 @@ StartBufferIO(BufferDesc *buf, bool forInput)
if (!(buf_state & BM_IO_IN_PROGRESS))
break;
UnlockBufHdr(buf, buf_state);
+ if (nowait)
+ return false;
WaitIO(buf);
}
diff --git a/src/backend/storage/buffer/localbuf.c b/src/backend/storage/buffer/localbuf.c
index fcfac335a57..985a2c7049c 100644
--- a/src/backend/storage/buffer/localbuf.c
+++ b/src/backend/storage/buffer/localbuf.c
@@ -108,10 +108,9 @@ PrefetchLocalBuffer(SMgrRelation smgr, ForkNumber forkNum,
* LocalBufferAlloc -
* Find or create a local buffer for the given page of the given relation.
*
- * API is similar to bufmgr.c's BufferAlloc, except that we do not need
- * to do any locking since this is all local. Also, IO_IN_PROGRESS
- * does not get set. Lastly, we support only default access strategy
- * (hence, usage_count is always advanced).
+ * API is similar to bufmgr.c's BufferAlloc, except that we do not need to do
+ * any locking since this is all local. We support only default access
+ * strategy (hence, usage_count is always advanced).
*/
BufferDesc *
LocalBufferAlloc(SMgrRelation smgr, ForkNumber forkNum, BlockNumber blockNum,
@@ -287,7 +286,7 @@ GetLocalVictimBuffer(void)
}
/* see LimitAdditionalPins() */
-static void
+void
LimitAdditionalLocalPins(uint32 *additional_pins)
{
uint32 max_pins;
@@ -297,9 +296,10 @@ LimitAdditionalLocalPins(uint32 *additional_pins)
/*
* In contrast to LimitAdditionalPins() other backends don't play a role
- * here. We can allow up to NLocBuffer pins in total.
+ * here. We can allow up to NLocBuffer pins in total, but it might not be
+ * initialized yet so read num_temp_buffers.
*/
- max_pins = (NLocBuffer - NLocalPinnedBuffers);
+ max_pins = (num_temp_buffers - NLocalPinnedBuffers);
if (*additional_pins >= max_pins)
*additional_pins = max_pins;
diff --git a/src/backend/storage/meson.build b/src/backend/storage/meson.build
index 40345bdca27..739d13293fb 100644
--- a/src/backend/storage/meson.build
+++ b/src/backend/storage/meson.build
@@ -1,5 +1,6 @@
# Copyright (c) 2022-2024, PostgreSQL Global Development Group
+subdir('aio')
subdir('buffer')
subdir('file')
subdir('freespace')
diff --git a/src/backend/utils/misc/guc_tables.c b/src/backend/utils/misc/guc_tables.c
index 1e71e7db4a0..71889471266 100644
--- a/src/backend/utils/misc/guc_tables.c
+++ b/src/backend/utils/misc/guc_tables.c
@@ -3112,6 +3112,20 @@ struct config_int ConfigureNamesInt[] =
NULL
},
+ {
+ {"buffer_io_size",
+ PGC_USERSET,
+ RESOURCES_ASYNCHRONOUS,
+ gettext_noop("Target size for coalescing reads and writes of buffered data blocks."),
+ NULL,
+ GUC_UNIT_BLOCKS
+ },
+ &buffer_io_size,
+ DEFAULT_BUFFER_IO_SIZE,
+ 1, MAX_BUFFER_IO_SIZE,
+ NULL, NULL, NULL
+ },
+
{
{"backend_flush_after", PGC_USERSET, RESOURCES_ASYNCHRONOUS,
gettext_noop("Number of pages after which previously performed writes are flushed to disk."),
diff --git a/src/backend/utils/misc/postgresql.conf.sample b/src/backend/utils/misc/postgresql.conf.sample
index 2244ee52f79..b7a4143df21 100644
--- a/src/backend/utils/misc/postgresql.conf.sample
+++ b/src/backend/utils/misc/postgresql.conf.sample
@@ -203,6 +203,7 @@
#backend_flush_after = 0 # measured in pages, 0 disables
#effective_io_concurrency = 1 # 1-1000; 0 disables prefetching
#maintenance_io_concurrency = 10 # 1-1000; 0 disables prefetching
+#buffer_io_size = 128kB
#max_worker_processes = 8 # (change requires restart)
#max_parallel_workers_per_gather = 2 # limited by max_parallel_workers
#max_parallel_maintenance_workers = 2 # limited by max_parallel_workers
diff --git a/doc/src/sgml/config.sgml b/doc/src/sgml/config.sgml
index 65a6e6c4086..3af86c59384 100644
--- a/doc/src/sgml/config.sgml
+++ b/doc/src/sgml/config.sgml
@@ -2719,6 +2719,20 @@ include_dir 'conf.d'
</listitem>
</varlistentry>
+ <varlistentry id="guc-buffer-io-size" xreflabel="buffer_io_size">
+ <term><varname>buffer_io_size</varname> (<type>integer</type>)
+ <indexterm>
+ <primary><varname>buffer_io_size</varname> configuration parameter</primary>
+ </indexterm>
+ </term>
+ <listitem>
+ <para>
+ Controls the target I/O size in operations that coalesce buffer I/O.
+ The default is 128kB.
+ </para>
+ </listitem>
+ </varlistentry>
+
<varlistentry id="guc-max-worker-processes" xreflabel="max_worker_processes">
<term><varname>max_worker_processes</varname> (<type>integer</type>)
<indexterm>
diff --git a/src/tools/pgindent/typedefs.list b/src/tools/pgindent/typedefs.list
index 4679660837c..a603b52ed70 100644
--- a/src/tools/pgindent/typedefs.list
+++ b/src/tools/pgindent/typedefs.list
@@ -2287,6 +2287,7 @@ ReInitializeDSMForeignScan_function
ReScanForeignScan_function
ReadBufPtrType
ReadBufferMode
+ReadBuffersOperation
ReadBytePtrType
ReadExtraTocPtrType
ReadFunc
@@ -2693,6 +2694,7 @@ StopList
StrategyNumber
StreamCtl
StreamStopReason
+StreamingRead
String
StringInfo
StringInfoData
--
2.43.0
From c7500cc1b9068ff0b704181442999cd8bed58658 Mon Sep 17 00:00:00 2001
From: Nazir Bilal Yavuz <byavu...@gmail.com>
Date: Mon, 19 Feb 2024 14:30:47 +0300
Subject: [PATCH v3 2/2] Use streaming read API in ANALYZE
ANALYZE command gets random tuples using BlockSampler algorithm. Use
streaming reads to get these tuples by using BlockSampler algorithm in
streaming read API prefetch logic.
---
src/include/access/tableam.h | 16 ++--
src/backend/access/heap/heapam_handler.c | 11 +--
src/backend/commands/analyze.c | 97 ++++++++----------------
3 files changed, 45 insertions(+), 79 deletions(-)
diff --git a/src/include/access/tableam.h b/src/include/access/tableam.h
index fc0e7027157..d83c085afca 100644
--- a/src/include/access/tableam.h
+++ b/src/include/access/tableam.h
@@ -21,6 +21,7 @@
#include "access/sdir.h"
#include "access/xact.h"
#include "executor/tuptable.h"
+#include "storage/streaming_read.h"
#include "utils/rel.h"
#include "utils/snapshot.h"
@@ -659,9 +660,9 @@ typedef struct TableAmRoutine
BufferAccessStrategy bstrategy);
/*
- * Prepare to analyze block `blockno` of `scan`. The scan has been started
- * with table_beginscan_analyze(). See also
- * table_scan_analyze_next_block().
+ * Prepare to analyze next block of `scan`. Next block is decided by
+ * callback function of `pgsr`. The scan has been started with
+ * table_beginscan_analyze(). See also table_scan_analyze_next_block().
*
* The callback may acquire resources like locks that are held until
* table_scan_analyze_next_tuple() returns false. It e.g. can make sense
@@ -676,8 +677,7 @@ typedef struct TableAmRoutine
* isn't one yet.
*/
bool (*scan_analyze_next_block) (TableScanDesc scan,
- BlockNumber blockno,
- BufferAccessStrategy bstrategy);
+ StreamingRead *stream);
/*
* See table_scan_analyze_next_tuple().
@@ -1755,11 +1755,9 @@ table_relation_vacuum(Relation rel, struct VacuumParams *params,
* Returns false if block is unsuitable for sampling, true otherwise.
*/
static inline bool
-table_scan_analyze_next_block(TableScanDesc scan, BlockNumber blockno,
- BufferAccessStrategy bstrategy)
+table_scan_analyze_next_block(TableScanDesc scan, StreamingRead *stream)
{
- return scan->rs_rd->rd_tableam->scan_analyze_next_block(scan, blockno,
- bstrategy);
+ return scan->rs_rd->rd_tableam->scan_analyze_next_block(scan, stream);
}
/*
diff --git a/src/backend/access/heap/heapam_handler.c b/src/backend/access/heap/heapam_handler.c
index 6abfe36dec7..0c285213dc8 100644
--- a/src/backend/access/heap/heapam_handler.c
+++ b/src/backend/access/heap/heapam_handler.c
@@ -1053,10 +1053,10 @@ heapam_relation_copy_for_cluster(Relation OldHeap, Relation NewHeap,
}
static bool
-heapam_scan_analyze_next_block(TableScanDesc scan, BlockNumber blockno,
- BufferAccessStrategy bstrategy)
+heapam_scan_analyze_next_block(TableScanDesc scan, StreamingRead *stream)
{
HeapScanDesc hscan = (HeapScanDesc) scan;
+ BlockNumber *current_block;
/*
* We must maintain a pin on the target page's buffer to ensure that
@@ -1067,10 +1067,11 @@ heapam_scan_analyze_next_block(TableScanDesc scan, BlockNumber blockno,
* doing much work per tuple, the extra lock traffic is probably better
* avoided.
*/
- hscan->rs_cblock = blockno;
+ hscan->rs_cbuf = streaming_read_buffer_next(stream, (void **) ¤t_block);
+ hscan->rs_cblock = *current_block;
hscan->rs_cindex = FirstOffsetNumber;
- hscan->rs_cbuf = ReadBufferExtended(scan->rs_rd, MAIN_FORKNUM,
- blockno, RBM_NORMAL, bstrategy);
+
+ Assert(BufferIsValid(hscan->rs_cbuf));
LockBuffer(hscan->rs_cbuf, BUFFER_LOCK_SHARE);
/* in heap all blocks can contain tuples, so always return true */
diff --git a/src/backend/commands/analyze.c b/src/backend/commands/analyze.c
index 8a82af4a4ca..bdad87c3a3e 100644
--- a/src/backend/commands/analyze.c
+++ b/src/backend/commands/analyze.c
@@ -1102,6 +1102,26 @@ examine_attribute(Relation onerel, int attnum, Node *index_expr)
return stats;
}
+/*
+ * Prefetch callback function to get next block number while using
+ * BlockSampling algorithm
+ */
+static BlockNumber
+pg_block_sampling_streaming_read_next(StreamingRead *stream,
+ void *user_data,
+ void *per_buffer_data)
+{
+ BlockSamplerData *bs = user_data;
+ BlockNumber *current_block = per_buffer_data;
+
+ if (BlockSampler_HasMore(bs))
+ *current_block = BlockSampler_Next(bs);
+ else
+ *current_block = InvalidBlockNumber;
+
+ return *current_block;
+}
+
/*
* acquire_sample_rows -- acquire a random sample of rows from the table
*
@@ -1154,10 +1174,7 @@ acquire_sample_rows(Relation onerel, int elevel,
TableScanDesc scan;
BlockNumber nblocks;
BlockNumber blksdone = 0;
-#ifdef USE_PREFETCH
- int prefetch_maximum = 0; /* blocks to prefetch if enabled */
- BlockSamplerData prefetch_bs;
-#endif
+ StreamingRead *stream;
Assert(targrows > 0);
@@ -1170,13 +1187,6 @@ acquire_sample_rows(Relation onerel, int elevel,
randseed = pg_prng_uint32(&pg_global_prng_state);
nblocks = BlockSampler_Init(&bs, totalblocks, targrows, randseed);
-#ifdef USE_PREFETCH
- prefetch_maximum = get_tablespace_maintenance_io_concurrency(onerel->rd_rel->reltablespace);
- /* Create another BlockSampler, using the same seed, for prefetching */
- if (prefetch_maximum)
- (void) BlockSampler_Init(&prefetch_bs, totalblocks, targrows, randseed);
-#endif
-
/* Report sampling block numbers */
pgstat_progress_update_param(PROGRESS_ANALYZE_BLOCKS_TOTAL,
nblocks);
@@ -1187,68 +1197,23 @@ acquire_sample_rows(Relation onerel, int elevel,
scan = table_beginscan_analyze(onerel);
slot = table_slot_create(onerel, NULL);
-#ifdef USE_PREFETCH
-
- /*
- * If we are doing prefetching, then go ahead and tell the kernel about
- * the first set of pages we are going to want. This also moves our
- * iterator out ahead of the main one being used, where we will keep it so
- * that we're always pre-fetching out prefetch_maximum number of blocks
- * ahead.
- */
- if (prefetch_maximum)
- {
- for (int i = 0; i < prefetch_maximum; i++)
- {
- BlockNumber prefetch_block;
-
- if (!BlockSampler_HasMore(&prefetch_bs))
- break;
-
- prefetch_block = BlockSampler_Next(&prefetch_bs);
- PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, prefetch_block);
- }
- }
-#endif
+ stream = streaming_read_buffer_begin(STREAMING_READ_MAINTENANCE,
+ vac_strategy,
+ BMR_REL(scan->rs_rd),
+ MAIN_FORKNUM,
+ pg_block_sampling_streaming_read_next,
+ &bs,
+ sizeof(BlockSamplerData));
/* Outer loop over blocks to sample */
- while (BlockSampler_HasMore(&bs))
+ while (nblocks)
{
bool block_accepted;
- BlockNumber targblock = BlockSampler_Next(&bs);
-#ifdef USE_PREFETCH
- BlockNumber prefetch_targblock = InvalidBlockNumber;
-
- /*
- * Make sure that every time the main BlockSampler is moved forward
- * that our prefetch BlockSampler also gets moved forward, so that we
- * always stay out ahead.
- */
- if (prefetch_maximum && BlockSampler_HasMore(&prefetch_bs))
- prefetch_targblock = BlockSampler_Next(&prefetch_bs);
-#endif
vacuum_delay_point();
- block_accepted = table_scan_analyze_next_block(scan, targblock, vac_strategy);
+ block_accepted = table_scan_analyze_next_block(scan, stream);
-#ifdef USE_PREFETCH
-
- /*
- * When pre-fetching, after we get a block, tell the kernel about the
- * next one we will want, if there's any left.
- *
- * We want to do this even if the table_scan_analyze_next_block() call
- * above decides against analyzing the block it picked.
- */
- if (prefetch_maximum && prefetch_targblock != InvalidBlockNumber)
- PrefetchBuffer(scan->rs_rd, MAIN_FORKNUM, prefetch_targblock);
-#endif
-
- /*
- * Don't analyze if table_scan_analyze_next_block() indicated this
- * block is unsuitable for analyzing.
- */
if (!block_accepted)
continue;
@@ -1299,7 +1264,9 @@ acquire_sample_rows(Relation onerel, int elevel,
pgstat_progress_update_param(PROGRESS_ANALYZE_BLOCKS_DONE,
++blksdone);
+ nblocks--;
}
+ streaming_read_buffer_end(stream);
ExecDropSingleTupleTableSlot(slot);
table_endscan(scan);
--
2.43.0
