On Wed, Feb 3, 2021 at 08:07:16PM -0500, Bruce Momjian wrote:
> > > I can try to add a hint-bit-page-write page counter, but that might
> > > overflow, and then we will need a way to change the LSN anyway.
> >
> > That's just a question of width...
>
> Yeah, the hint bit counter is just delaying the inevitable, plus it
> changes the page format, which I am trying to avoid. Also, I need this
> dummy record only if the page is marked clean, meaning a write
> to the file system already happened in the current checkpoint --- should
> not be to bad.
Here is a proof-of-concept patch to do this. Thanks for your help.
--
Bruce Momjian <br...@momjian.us> https://momjian.us
EDB https://enterprisedb.com
The usefulness of a cup is in its emptiness, Bruce Lee
>From 11cb0ca7405a74105602fd63766e88c1fea8ea30 Mon Sep 17 00:00:00 2001
From: Bruce Momjian <br...@momjian.us>
Date: Wed, 3 Feb 2021 22:25:39 -0500
Subject: [PATCH] hint squash commit
---
src/backend/access/rmgrdesc/xlogdesc.c | 6 +++++-
src/backend/access/transam/xlog.c | 4 ++++
src/backend/access/transam/xloginsert.c | 26 ++++++++++++++++++++++++
src/backend/replication/logical/decode.c | 1 +
src/backend/storage/buffer/bufmgr.c | 18 ++++++++++++++++
src/include/access/xloginsert.h | 2 ++
src/include/catalog/pg_control.h | 1 +
7 files changed, 57 insertions(+), 1 deletion(-)
diff --git a/src/backend/access/rmgrdesc/xlogdesc.c b/src/backend/access/rmgrdesc/xlogdesc.c
index 92cc7ea073..16a967bb71 100644
--- a/src/backend/access/rmgrdesc/xlogdesc.c
+++ b/src/backend/access/rmgrdesc/xlogdesc.c
@@ -80,7 +80,8 @@ xlog_desc(StringInfo buf, XLogReaderState *record)
appendStringInfoString(buf, xlrec->rp_name);
}
- else if (info == XLOG_FPI || info == XLOG_FPI_FOR_HINT)
+ else if (info == XLOG_FPI || info == XLOG_FPI_FOR_HINT ||
+ info == XLOG_HINT_LSN)
{
/* no further information to print */
}
@@ -185,6 +186,9 @@ xlog_identify(uint8 info)
case XLOG_FPI_FOR_HINT:
id = "FPI_FOR_HINT";
break;
+ case XLOG_HINT_LSN:
+ id = "HINT_LSN";
+ break;
}
return id;
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index f03bd473e2..f67316ee07 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -10260,6 +10260,10 @@ xlog_redo(XLogReaderState *record)
UnlockReleaseBuffer(buffer);
}
}
+ else if (info == XLOG_HINT_LSN)
+ {
+ /* nothing to do here */
+ }
else if (info == XLOG_BACKUP_END)
{
XLogRecPtr startpoint;
diff --git a/src/backend/access/transam/xloginsert.c b/src/backend/access/transam/xloginsert.c
index 7052dc245e..eebca0fc16 100644
--- a/src/backend/access/transam/xloginsert.c
+++ b/src/backend/access/transam/xloginsert.c
@@ -980,6 +980,32 @@ XLogSaveBufferForHint(Buffer buffer, bool buffer_std)
return recptr;
}
+/*
+ * On the first hint bit change during a checkpoint, XLogSaveBufferForHint()
+ * writes a full page image to the WAL and returns a new LSN which can be
+ * assigned to the page. Cluster file encryption needs a new LSN for
+ * every hint bit page write because the LSN is used in the nonce, and
+ * the nonce must be unique. Therefore, this routine just advances the LSN
+ * so the page can be assigned a new LSN.
+ *
+ * Callable while holding just share lock on the buffer content.
+ *
+ * The LSN of the inserted wal record is returned if we had to write,
+ * InvalidXLogRecPtr otherwise.
+ *
+ * It is possible that multiple concurrent backends could attempt to write WAL
+ * records. In that case, multiple copies of the same block would be recorded
+ * in separate WAL records by different backends, though that is still OK from
+ * a correctness perspective.
+ */
+XLogRecPtr
+XLogLSNForHint(void)
+{
+ XLogBeginInsert();
+
+ return XLogInsert(RM_XLOG_ID, XLOG_HINT_LSN);
+}
+
/*
* Write a WAL record containing a full image of a page. Caller is responsible
* for writing the page to disk after calling this routine.
diff --git a/src/backend/replication/logical/decode.c b/src/backend/replication/logical/decode.c
index afa1df00d0..2ada89c6b1 100644
--- a/src/backend/replication/logical/decode.c
+++ b/src/backend/replication/logical/decode.c
@@ -223,6 +223,7 @@ DecodeXLogOp(LogicalDecodingContext *ctx, XLogRecordBuffer *buf)
case XLOG_FPW_CHANGE:
case XLOG_FPI_FOR_HINT:
case XLOG_FPI:
+ case XLOG_HINT_LSN:
break;
default:
elog(ERROR, "unexpected RM_XLOG_ID record type: %u", info);
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c
index 561c212092..fd59f9fc1d 100644
--- a/src/backend/storage/buffer/bufmgr.c
+++ b/src/backend/storage/buffer/bufmgr.c
@@ -3865,6 +3865,24 @@ MarkBufferDirtyHint(Buffer buffer, bool buffer_std)
{
dirtied = true; /* Means "will be dirtied by this action" */
+ /*
+ * If the buffer is clean, and lsn is valid, it must be the
+ * first hint bit change of the checkpoint (the old page lsn
+ * is earlier than the RedoRecPtr). If the page is clean and
+ * the lsn is invalid, the page must have been already written
+ * during this checkpoint, and this is a new hint bit change.
+ * Such page changes usually don't create new page lsns, but we
+ * need one for cluster file encryption because the lsn is used as
+ * part of the nonce, and we don't want to reencrypt the page
+ * with the hint bit changes using the same nonce as the previous
+ * writes during this checkpoint. (It would expose the hint bit
+ * change locations.) Therefore we create a simple WAL record
+ * to advance the lsn, which can can then be assigned to the
+ * page.
+ */
+ if (XLogRecPtrIsInvalid(lsn) /* XXX && file_encryption_method != 0 */)
+ lsn = XLogLSNForHint();
+
/*
* Set the page LSN if we wrote a backup block. We aren't supposed
* to set this when only holding a share lock but as long as we
diff --git a/src/include/access/xloginsert.h b/src/include/access/xloginsert.h
index f1d8c39edf..a066f65229 100644
--- a/src/include/access/xloginsert.h
+++ b/src/include/access/xloginsert.h
@@ -61,6 +61,8 @@ extern void log_newpage_range(Relation rel, ForkNumber forkNum,
BlockNumber startblk, BlockNumber endblk, bool page_std);
extern XLogRecPtr XLogSaveBufferForHint(Buffer buffer, bool buffer_std);
+extern XLogRecPtr XLogLSNForHint(void);
+
extern void InitXLogInsert(void);
#endif /* XLOGINSERT_H */
diff --git a/src/include/catalog/pg_control.h b/src/include/catalog/pg_control.h
index e3f48158ce..36ac7dfbb8 100644
--- a/src/include/catalog/pg_control.h
+++ b/src/include/catalog/pg_control.h
@@ -76,6 +76,7 @@ typedef struct CheckPoint
#define XLOG_END_OF_RECOVERY 0x90
#define XLOG_FPI_FOR_HINT 0xA0
#define XLOG_FPI 0xB0
+#define XLOG_HINT_LSN 0xC0
/*
--
2.20.1
