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tests: Make neon_xlogflush() flush all WAL, if you omit the LSN arg

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This makes it much more convenient to use in the common case that you
want to flush all the WAL. (Passing pg_current_wal_insert_lsn() as the
argument doesn't work for the same reasons as explained in the
comments: we need to be back off to the beginning of a page if the
previous record ended at page boundary.)

I plan to use this to fix the issue that Arseny Sher called out at
https://github.com/neondatabase/neon/pull/7288#discussion_r1660063852
This commit is contained in:
Heikki Linnakangas
2024-07-01 12:58:08 +03:00
parent 57535c039c
commit 75c84c846a
4 changed files with 40 additions and 4 deletions
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2
pgxn/neon_test_utils/Makefile
View File

@@ -7,7 +7,7 @@ OBJS = \
neontest.o
EXTENSION = neon_test_utils
DATA = neon_test_utils--1.1.sql
DATA = neon_test_utils--1.2.sql
PGFILEDESC = "neon_test_utils - helpers for neon testing and debugging"
PG_CONFIG = pg_config

2
pgxn/neon_test_utils/neon_test_utils--1.1.sql → pgxn/neon_test_utils/neon_test_utils--1.2.sql
View File

@@ -41,7 +41,7 @@ RETURNS bytea
AS 'MODULE_PATHNAME', 'get_raw_page_at_lsn_ex'
LANGUAGE C PARALLEL UNSAFE;
CREATE FUNCTION neon_xlogflush(lsn pg_lsn)
CREATE FUNCTION neon_xlogflush(lsn pg_lsn DEFAULT NULL)
RETURNS VOID
AS 'MODULE_PATHNAME', 'neon_xlogflush'
LANGUAGE C PARALLEL UNSAFE;

2
pgxn/neon_test_utils/neon_test_utils.control
View File

@@ -1,6 +1,6 @@
# neon_test_utils extension
comment = 'helpers for neon testing and debugging'
default_version = '1.1'
default_version = '1.2'
module_pathname = '$libdir/neon_test_utils'
relocatable = true
trusted = true

38
pgxn/neon_test_utils/neontest.c
View File

@@ -15,6 +15,7 @@
#include "access/relation.h"
#include "access/xact.h"
#include "access/xlog.h"
#include "access/xlog_internal.h"
#include "catalog/namespace.h"
#include "fmgr.h"
#include "funcapi.h"
@@ -444,11 +445,46 @@ get_raw_page_at_lsn_ex(PG_FUNCTION_ARGS)
/*
* Directly calls XLogFlush(lsn) to flush WAL buffers.
*
* If 'lsn' is not specified (is NULL), flush all generated WAL.
*/
Datum
neon_xlogflush(PG_FUNCTION_ARGS)
{
XLogRecPtr lsn = PG_GETARG_LSN(0);
XLogRecPtr lsn;
if (RecoveryInProgress())
ereport(ERROR,
(errcode(ERRCODE_OBJECT_NOT_IN_PREREQUISITE_STATE),
errmsg("recovery is in progress"),
errhint("cannot flush WAL during recovery.")));
if (!PG_ARGISNULL(0))
lsn = PG_GETARG_LSN(0);
else
{
lsn = GetXLogInsertRecPtr();
/*---
* The LSN returned by GetXLogInsertRecPtr() is the position where the
* next inserted record would begin. If the last record ended just at
* the page boundary, the next record will begin after the page header
* on the next page, and that's what GetXLogInsertRecPtr().returns,
* but the page header has not been written yet. If we tried to flush
* it, XLogFlush() would throw an error:
*
* ERROR : xlog flush request %X/%X is not satisfied --- flushed only to %X/%X
*
* To avoid that, if the insert position points to just after the page
* header, back off to page boundary.
*/
if (lsn % XLOG_BLCKSZ == SizeOfXLogShortPHD &&
XLogSegmentOffset(lsn, wal_segment_size) > XLOG_BLCKSZ)
lsn -= SizeOfXLogShortPHD;
else if (lsn % XLOG_BLCKSZ == SizeOfXLogLongPHD &&
XLogSegmentOffset(lsn, wal_segment_size) < XLOG_BLCKSZ)
lsn -= SizeOfXLogLongPHD;
}
XLogFlush(lsn);
PG_RETURN_VOID();