Dear All,
I would propose a new function like GetXLogInsertRecPtr(), but with some
modifications (please, see the attached patch). The result LSN can be passed to
XLogFLush() safely. I believe, it will not raise an error in any case.
XLogFlush(GetXLogLastInsertEndRecPtr()) will flush (fsync) all already inserted
records at the moment. It is what I would like to get.
I'm not sure, we need a SQL function counterpart for this new C function, but
it is not a big deal to implement.
With best regards,
Vitaly
On Monday, August 19, 2024 09:35 MSK, Michael Paquier <mich...@paquier.xyz>
wrote:
On Wed, Aug 07, 2024 at 06:00:45PM +0300, Aleksander Alekseev wrote:
> Assuming the function has value, as you claim, I see no reason not to
> expose it similarly to pg_current_wal_*(). On top of that you will
> have to test-cover it anyway. The easiest way to do it will be to have
> an SQL-wrapper.
I cannot be absolutely without seeing a patch, but adding SQL
functions in this area is usually very useful for monitoring purposes
of external solutions.
--
Michael
From ba82d6c6f8570fbbff14b4b52fa7720122bfb8ad Mon Sep 17 00:00:00 2001
From: Vitaly Davydov <v.davy...@postgrespro.ru>
Date: Tue, 20 Aug 2024 18:03:11 +0300
Subject: [PATCH] Add function to return the end LSN of the last inserted WAL
record
---
src/backend/access/transam/xlog.c | 19 +++++++++++++++++++
src/include/access/xlog.h | 1 +
2 files changed, 20 insertions(+)
diff --git a/src/backend/access/transam/xlog.c b/src/backend/access/transam/xlog.c
index ee0fb0e28f..1430aea6d5 100644
--- a/src/backend/access/transam/xlog.c
+++ b/src/backend/access/transam/xlog.c
@@ -9425,6 +9425,25 @@ GetXLogWriteRecPtr(void)
return LogwrtResult.Write;
}
+/*
+ * Get the end pointer of the last inserted WAL record.
+ * The returned value will differ from the current insert pointer
+ * returned by GetXLogInsertRecPtr() if the last WAL record ends
+ * up at a page boundary.
+ */
+XLogRecPtr
+GetXLogLastInsertEndRecPtr(void)
+{
+ XLogCtlInsert *Insert = &XLogCtl->Insert;
+ uint64 current_bytepos;
+
+ SpinLockAcquire(&Insert->insertpos_lck);
+ current_bytepos = Insert->CurrBytePos;
+ SpinLockRelease(&Insert->insertpos_lck);
+
+ return XLogBytePosToEndRecPtr(current_bytepos);
+}
+
/*
* Returns the redo pointer of the last checkpoint or restartpoint. This is
* the oldest point in WAL that we still need, if we have to restart recovery.
diff --git a/src/include/access/xlog.h b/src/include/access/xlog.h
index 083810f5b4..e98a825642 100644
--- a/src/include/access/xlog.h
+++ b/src/include/access/xlog.h
@@ -226,6 +226,7 @@ extern RecoveryState GetRecoveryState(void);
extern bool XLogInsertAllowed(void);
extern XLogRecPtr GetXLogInsertRecPtr(void);
extern XLogRecPtr GetXLogWriteRecPtr(void);
+extern XLogRecPtr GetXLogLastInsertEndRecPtr(void);
extern uint64 GetSystemIdentifier(void);
extern char *GetMockAuthenticationNonce(void);
--
2.34.1
