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Fix ALTER TABLE ... SET TABLESPACE for unlogged relations.

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Changing the tablespace of an unlogged relation did not WAL log the
creation and content of the init fork. Thus, after a standby is
promoted, unlogged relation cannot be accessed anymore, with errors
like:
ERROR:  58P01: could not open file "pg_tblspc/...": No such file or directory
Additionally the init fork was not synced to disk, independent of the
configured wal_level, a relatively small durability risk.

Investigation of that problem also brought to light that, even for
permanent relations, the creation of !main forks was not WAL logged,
i.e. no XLOG_SMGR_CREATE record were emitted. That mostly turns out not
to be a problem, because these files were created when the actual
relation data is copied; nonexistent files are not treated as an error
condition during replay. But that doesn't work for empty files, and
generally feels a bit haphazard. Luckily, outside init and main forks,
empty forks don't occur often or are not a problem.

Add the required WAL logging and syncing to disk.

Reported-By: Michael Paquier
Author: Michael Paquier and Andres Freund
Discussion: 20151210163230.GA11331@alap3.anarazel.de
Backpatch: 9.1, where unlogged relations were introduced
This commit is contained in:
Andres Freund 2015-12-12 14:19:19 +01:00
parent ea7f7d8b32
commit ada9c09aeb
1 changed files with 22 additions and 2 deletions
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24
src/backend/commands/tablecmds.c
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@ -42,6 +42,7 @@
#include "catalog/pg_type.h"
#include "catalog/pg_type_fn.h"
#include "catalog/storage.h"
#include "catalog/storage_xlog.h"
#include "catalog/toasting.h"
#include "commands/cluster.h"
#include "commands/comment.h"
@ -9635,6 +9636,15 @@ ATExecSetTableSpace(Oid tableOid, Oid newTableSpace, LOCKMODE lockmode)
if (smgrexists(rel->rd_smgr, forkNum))
{
smgrcreate(dstrel, forkNum, false);
/*
* WAL log creation if the relation is persistent, or this is the
* init fork of an unlogged relation.
*/
if (rel->rd_rel->relpersistence == RELPERSISTENCE_PERMANENT ||
(rel->rd_rel->relpersistence == RELPERSISTENCE_UNLOGGED &&
forkNum == INIT_FORKNUM))
log_smgrcreate(&newrnode, forkNum);
copy_relation_data(rel->rd_smgr, dstrel, forkNum,
rel->rd_rel->relpersistence);
}
@ -9854,6 +9864,7 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
char *buf;
Page page;
bool use_wal;
bool copying_initfork;
BlockNumber nblocks;
BlockNumber blkno;
@ -9866,11 +9877,20 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
buf = (char *) palloc(BLCKSZ);
page = (Page) buf;
/*
* The init fork for an unlogged relation in many respects has to be
* treated the same as normal relation, changes need to be WAL logged and
* it needs to be synced to disk.
*/
copying_initfork = relpersistence == RELPERSISTENCE_UNLOGGED &&
forkNum == INIT_FORKNUM;
/*
* We need to log the copied data in WAL iff WAL archiving/streaming is
* enabled AND it's a permanent relation.
*/
use_wal = XLogIsNeeded() && relpersistence == RELPERSISTENCE_PERMANENT;
use_wal = XLogIsNeeded() &&
(relpersistence == RELPERSISTENCE_PERMANENT || copying_initfork);
nblocks = smgrnblocks(src, forkNum);
@ -9925,7 +9945,7 @@ copy_relation_data(SMgrRelation src, SMgrRelation dst,
* wouldn't replay our earlier WAL entries. If we do not fsync those pages
* here, they might still not be on disk when the crash occurs.
*/
if (relpersistence == RELPERSISTENCE_PERMANENT)
if (relpersistence == RELPERSISTENCE_PERMANENT || copying_initfork)
smgrimmedsync(dst, forkNum);
}