On Fri, Jan 28, 2022 at 7:47 PM Andres Freund <and...@anarazel.de> wrote:
>
> On 2022-01-28 16:36:32 -0800, Andres Freund wrote:
> > On 2022-01-28 18:43:57 -0500, James Coleman wrote:
> > > Alternatively I see pg_attribute_aligned, but that's not defined
> > > (AFAICT) on clang, for example, so I'm not sure that'd be acceptable?
> >
> > clang should have it (it defines __GNUC__). The problem would be msvc, I
> > think. Not sure if there's a way to get to a common way of defining it
> > between
> > gcc-like compilers and msvc (the rest is niche enough that we don't need to
> > care about the efficiency I think).
>
> Seems like it's doable:
>
> https://godbolt.org/z/3c5573bTW
Oh, thanks. I'd seen some discussion previously on the list about
clang not supporting it, but that seems to have been incorrect. Also I
didn't know about that compiler site -- that's really neat.
Here's an updated patch series using that approach; the first patch
can (and probably should be) committed separately/regardless to update
the pg_attribute_aligned to be used in MSVC.
Thanks,
James Coleman
From c104bec6ed93cea06f4d5ff0f9150490f159dfaa Mon Sep 17 00:00:00 2001
From: jcoleman <jtc...@gmail.com>
Date: Sat, 29 Jan 2022 11:28:45 -0500
Subject: [PATCH v4 1/2] Support pg_attribute_aligned in MSVC
---
configure | 2 ++
src/include/c.h | 4 ++++
2 files changed, 6 insertions(+)
diff --git a/configure b/configure
index 3f2aea0d7d..e9ab674f38 100755
--- a/configure
+++ b/configure
@@ -17862,6 +17862,8 @@ else
/* This must match the corresponding code in c.h: */
#if defined(__GNUC__) || defined(__SUNPRO_C) || defined(__IBMC__)
#define pg_attribute_aligned(a) __attribute__((aligned(a)))
+#elif defined(_MSC_VER)
+#define pg_attribute_aligned(a) __declspec(align(a))
#endif
typedef __int128 int128a
#if defined(pg_attribute_aligned)
diff --git a/src/include/c.h b/src/include/c.h
index 4f16e589b3..0441b031b4 100644
--- a/src/include/c.h
+++ b/src/include/c.h
@@ -179,6 +179,10 @@
#define pg_attribute_noreturn()
#endif
+#if defined(_MSC_VER)
+#define pg_attribute_aligned(a) __declspec(align(a))
+#endif
+
/*
* Use "pg_attribute_always_inline" in place of "inline" for functions that
* we wish to force inlining of, even when the compiler's heuristics would
--
2.17.1
From 1f456c9f3976e49cc9be31878c5ad5d7eba5c1b6 Mon Sep 17 00:00:00 2001
From: jcoleman <jtc...@gmail.com>
Date: Sat, 29 Jan 2022 12:18:45 -0500
Subject: [PATCH v4 2/2] Expose LSN of last commit via pg_last_committed_xact
---
src/backend/access/transam/xact.c | 6 +++-
src/backend/access/transam/xlogfuncs.c | 17 ++++++++++
src/backend/storage/ipc/procarray.c | 34 +++++++++++++++++++
src/include/access/transam.h | 2 ++
src/include/catalog/pg_proc.dat | 6 ++++
src/include/storage/proc.h | 10 ++++++
src/include/storage/procarray.h | 2 ++
.../test_misc/t/002_last_commit_lsn.pl | 31 +++++++++++++++++
8 files changed, 107 insertions(+), 1 deletion(-)
create mode 100644 src/test/modules/test_misc/t/002_last_commit_lsn.pl
diff --git a/src/backend/access/transam/xact.c b/src/backend/access/transam/xact.c
index c9516e03fa..f2ae4b0667 100644
--- a/src/backend/access/transam/xact.c
+++ b/src/backend/access/transam/xact.c
@@ -1355,6 +1355,7 @@ RecordTransactionCommit(void)
else
{
bool replorigin;
+ XLogRecPtr commit_lsn;
/*
* Are we using the replication origins feature? Or, in other words,
@@ -1391,7 +1392,7 @@ RecordTransactionCommit(void)
SetCurrentTransactionStopTimestamp();
- XactLogCommitRecord(xactStopTimestamp,
+ commit_lsn = XactLogCommitRecord(xactStopTimestamp,
nchildren, children, nrels, rels,
nmsgs, invalMessages,
RelcacheInitFileInval,
@@ -1419,6 +1420,7 @@ RecordTransactionCommit(void)
TransactionTreeSetCommitTsData(xid, nchildren, children,
replorigin_session_origin_timestamp,
replorigin_session_origin);
+ MyProc->lastCommitLSN = commit_lsn;
}
/*
@@ -5883,6 +5885,8 @@ xact_redo_commit(xl_xact_parsed_commit *parsed,
TransactionTreeSetCommitTsData(xid, parsed->nsubxacts, parsed->subxacts,
commit_time, origin_id);
+ MyProc->lastCommitLSN = lsn;
+
if (standbyState == STANDBY_DISABLED)
{
/*
diff --git a/src/backend/access/transam/xlogfuncs.c b/src/backend/access/transam/xlogfuncs.c
index d8af5aad58..05ee661fc2 100644
--- a/src/backend/access/transam/xlogfuncs.c
+++ b/src/backend/access/transam/xlogfuncs.c
@@ -29,6 +29,7 @@
#include "replication/walreceiver.h"
#include "storage/fd.h"
#include "storage/ipc.h"
+#include "storage/procarray.h"
#include "storage/smgr.h"
#include "utils/builtins.h"
#include "utils/guc.h"
@@ -425,6 +426,22 @@ pg_last_wal_replay_lsn(PG_FUNCTION_ARGS)
PG_RETURN_LSN(recptr);
}
+/*
+ * pg_last_commit_lsn
+ *
+ * SQL-callable wrapper to obtain the lsn of the last commit.
+ */
+Datum
+pg_last_commit_lsn(PG_FUNCTION_ARGS)
+{
+ XLogRecPtr lsn = GetLastCommitLSN();
+
+ if (lsn == InvalidXLogRecPtr)
+ PG_RETURN_NULL();
+ else
+ PG_RETURN_DATUM(LSNGetDatum(lsn));
+}
+
/*
* Compute an xlog file name and decimal byte offset given a WAL location,
* such as is returned by pg_stop_backup() or pg_switch_wal().
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 3be6040289..92586d1492 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -430,6 +430,7 @@ CreateSharedProcArray(void)
procArray->replication_slot_xmin = InvalidTransactionId;
procArray->replication_slot_catalog_xmin = InvalidTransactionId;
ShmemVariableCache->xactCompletionCount = 1;
+ ShmemVariableCache->finishedProcsLastCommitLSN = InvalidXLogRecPtr;
}
allProcs = ProcGlobal->allProcs;
@@ -580,6 +581,9 @@ ProcArrayRemove(PGPROC *proc, TransactionId latestXid)
/* Same with xactCompletionCount */
ShmemVariableCache->xactCompletionCount++;
+ if (proc->lastCommitLSN > ShmemVariableCache->finishedProcsLastCommitLSN)
+ ShmemVariableCache->finishedProcsLastCommitLSN = proc->lastCommitLSN;
+
ProcGlobal->xids[myoff] = InvalidTransactionId;
ProcGlobal->subxidStates[myoff].overflowed = false;
ProcGlobal->subxidStates[myoff].count = 0;
@@ -3914,6 +3918,36 @@ ProcArrayGetReplicationSlotXmin(TransactionId *xmin,
LWLockRelease(ProcArrayLock);
}
+/*
+ * GetLastCommitLSN
+ *
+ * Return LSN of the most recent COMMIT record written to WAL.
+ *
+ * For performance reasons we do not guarantee the result to be perfectly in
+ * line with current visibility.
+ */
+XLogRecPtr
+GetLastCommitLSN(void)
+{
+ ProcArrayStruct *arrayP = procArray;
+ XLogRecPtr lsn;
+ int i;
+
+ LWLockAcquire(ProcArrayLock, LW_SHARED);
+ lsn = ShmemVariableCache->finishedProcsLastCommitLSN;
+ for (i = 0; i < arrayP->numProcs; i++)
+ {
+ int pgprocno = arrayP->pgprocnos[i];
+ PGPROC *proc = &allProcs[pgprocno];
+
+ if (proc->lastCommitLSN > lsn)
+ lsn = proc->lastCommitLSN;
+ }
+ LWLockRelease(ProcArrayLock);
+
+ return lsn;
+}
+
/*
* XidCacheRemoveRunningXids
*
diff --git a/src/include/access/transam.h b/src/include/access/transam.h
index 338dfca5a0..c53f2d3810 100644
--- a/src/include/access/transam.h
+++ b/src/include/access/transam.h
@@ -237,6 +237,8 @@ typedef struct VariableCacheData
*/
FullTransactionId latestCompletedXid; /* newest full XID that has
* committed or aborted */
+ /* */
+ XLogRecPtr finishedProcsLastCommitLSN;
/*
* Number of top-level transactions with xids (i.e. which may have
diff --git a/src/include/catalog/pg_proc.dat b/src/include/catalog/pg_proc.dat
index d6bf1f3274..cdf73f3bd5 100644
--- a/src/include/catalog/pg_proc.dat
+++ b/src/include/catalog/pg_proc.dat
@@ -6164,6 +6164,12 @@
proargnames => '{xid,timestamp,roident}',
prosrc => 'pg_last_committed_xact' },
+{ oid => '9861',
+ descr => 'get commit lsn of latest transaction commit',
+ proname => 'pg_last_commit_lsn', provolatile => 'v',
+ prorettype => 'pg_lsn', proargtypes => '',
+ prosrc => 'pg_last_commit_lsn' },
+
{ oid => '3537', descr => 'get identification of SQL object',
proname => 'pg_describe_object', provolatile => 's', prorettype => 'text',
proargtypes => 'oid oid int4', prosrc => 'pg_describe_object' },
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index a58888f9e9..efaf6442f5 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -258,6 +258,16 @@ struct PGPROC
PGPROC *lockGroupLeader; /* lock group leader, if I'm a member */
dlist_head lockGroupMembers; /* list of members, if I'm a leader */
dlist_node lockGroupLink; /* my member link, if I'm a member */
+
+ /*
+ * Last transaction metadata.
+ */
+#ifndef pg_attribute_aligned
+ char *pad[PG_CACHE_LINE_SIZE];
+#else
+ pg_attribute_aligned(PG_CACHE_LINE_SIZE)
+#endif
+ XLogRecPtr lastCommitLSN; /* cache of last committed LSN */
};
/* NOTE: "typedef struct PGPROC PGPROC" appears in storage/lock.h. */
diff --git a/src/include/storage/procarray.h b/src/include/storage/procarray.h
index e03692053e..ec3baa29e8 100644
--- a/src/include/storage/procarray.h
+++ b/src/include/storage/procarray.h
@@ -94,4 +94,6 @@ extern void ProcArraySetReplicationSlotXmin(TransactionId xmin,
extern void ProcArrayGetReplicationSlotXmin(TransactionId *xmin,
TransactionId *catalog_xmin);
+extern XLogRecPtr GetLastCommitLSN(void);
+
#endif /* PROCARRAY_H */
diff --git a/src/test/modules/test_misc/t/002_last_commit_lsn.pl b/src/test/modules/test_misc/t/002_last_commit_lsn.pl
new file mode 100644
index 0000000000..f249326c6b
--- /dev/null
+++ b/src/test/modules/test_misc/t/002_last_commit_lsn.pl
@@ -0,0 +1,31 @@
+
+# Copyright (c) 2021-2022, PostgreSQL Global Development Group
+
+use strict;
+use warnings;
+use PostgreSQL::Test::Cluster;
+use PostgreSQL::Test::Utils;
+use Test::More tests => 2;
+
+# Initialize a test cluster
+my $node = PostgreSQL::Test::Cluster->new('primary');
+$node->init();
+$node->start;
+
+my ($ret, $before_lsn, $after_lsn);
+
+$ret = $node->safe_psql('postgres', 'SELECT pg_last_commit_lsn()');
+is($ret, '', 'null at startup');
+
+$node->safe_psql('postgres', qq[CREATE TABLE t(i integer);]);
+
+$before_lsn = $node->safe_psql('postgres', 'SELECT pg_current_wal_lsn()');
+$node->safe_psql('postgres', 'INSERT INTO t(i) VALUES (1)');
+$after_lsn = $node->safe_psql('postgres', 'SELECT pg_current_wal_lsn()');
+
+$ret = $node->safe_psql('postgres', qq[
+ SELECT pg_last_commit_lsn() BETWEEN '$before_lsn'::pg_lsn AND '$after_lsn'::pg_lsn
+]);
+is($ret, 't', 'last commit lsn is set');
+
+$node->stop('fast');
--
2.17.1
