database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-08-24 09:27:52 +03:00
Code Activity

Fix race condition between hot standby and restoring a full-page image.

Browse Source 
There was a window in RestoreBackupBlock where a page would be zeroed out,
but not yet locked. If a backend pinned and locked the page in that window,
it saw the zeroed page instead of the old page or new page contents, which
could lead to missing rows in a result set, or errors.

To fix, replace RBM_ZERO with RBM_ZERO_AND_LOCK, which atomically pins,
zeroes, and locks the page, if it's not in the buffer cache already.

In stable branches, the old RBM_ZERO constant is renamed to RBM_DO_NOT_USE,
to avoid breaking any 3rd party extensions that might use RBM_ZERO. More
importantly, this avoids renumbering the other enum values, which would
cause even bigger confusion in extensions that use ReadBufferExtended, but
haven't been recompiled.

Backpatch to all supported versions; this has been racy since hot standby
was introduced.
This commit is contained in:
Heikki Linnakangas
2014-11-13 19:47:44 +02:00
parent 35fed51626
commit 81c4508196
5 changed files with 78 additions and 32 deletions
Download Patch File Download Diff File Expand all files Collapse all files

44
src/backend/access/transam/xlogutils.c
View File

@@ -287,9 +287,13 @@ XLogReadBufferForRedo(XLogRecPtr lsn, XLogRecord *record, int block_index,
* XLogReadBufferForRedoExtended
* Like XLogReadBufferForRedo, but with extra options.
*
* If mode is RBM_ZERO or RBM_ZERO_ON_ERROR, if the page doesn't exist, the
* relation is extended with all-zeroes pages up to the referenced block
* number. In RBM_ZERO mode, the return value is always BLK_NEEDS_REDO.
* In RBM_ZERO_* modes, if the page doesn't exist, the relation is extended
* with all-zeroes pages up to the referenced block number. In
* RBM_ZERO_AND_LOCK and RBM_ZERO_AND_CLEANUP_LOCK modes, the return value
* is always BLK_NEEDS_REDO.
*
* (The RBM_ZERO_AND_CLEANUP_LOCK mode is redundant with the get_cleanup_lock
* parameter. Do not use an inconsistent combination!)
*
* If 'get_cleanup_lock' is true, a "cleanup lock" is acquired on the buffer
* using LockBufferForCleanup(), instead of a regular exclusive lock.
@@ -312,10 +316,13 @@ XLogReadBufferForRedoExtended(XLogRecPtr lsn, XLogRecord *record,
*buf = XLogReadBufferExtended(rnode, forkno, blkno, mode);
if (BufferIsValid(*buf))
{
if (get_cleanup_lock)
LockBufferForCleanup(*buf);
else
LockBuffer(*buf, BUFFER_LOCK_EXCLUSIVE);
if (mode != RBM_ZERO_AND_LOCK && mode != RBM_ZERO_AND_CLEANUP_LOCK)
{
if (get_cleanup_lock)
LockBufferForCleanup(*buf);
else
LockBuffer(*buf, BUFFER_LOCK_EXCLUSIVE);
}
if (lsn <= PageGetLSN(BufferGetPage(*buf)))
return BLK_DONE;
else
@@ -341,7 +348,8 @@ XLogReadBufferForRedoExtended(XLogRecPtr lsn, XLogRecord *record,
* The returned buffer is exclusively-locked.
*
* For historical reasons, instead of a ReadBufferMode argument, this only
* supports RBM_ZERO (init == true) and RBM_NORMAL (init == false) modes.
* supports RBM_ZERO_AND_LOCK (init == true) and RBM_NORMAL (init == false)
* modes.
*/
Buffer
XLogReadBuffer(RelFileNode rnode, BlockNumber blkno, bool init)
@@ -349,8 +357,8 @@ XLogReadBuffer(RelFileNode rnode, BlockNumber blkno, bool init)
Buffer buf;
buf = XLogReadBufferExtended(rnode, MAIN_FORKNUM, blkno,
init ? RBM_ZERO : RBM_NORMAL);
if (BufferIsValid(buf))
init ? RBM_ZERO_AND_LOCK : RBM_NORMAL);
if (BufferIsValid(buf) && !init)
LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
return buf;
@@ -369,8 +377,8 @@ XLogReadBuffer(RelFileNode rnode, BlockNumber blkno, bool init)
* dropped or truncated. If we don't see evidence of that later in the WAL
* sequence, we'll complain at the end of WAL replay.)
*
* In RBM_ZERO and RBM_ZERO_ON_ERROR modes, if the page doesn't exist, the
* relation is extended with all-zeroes pages up to the given block number.
* In RBM_ZERO_* modes, if the page doesn't exist, the relation is extended
* with all-zeroes pages up to the given block number.
*
* In RBM_NORMAL_NO_LOG mode, we return InvalidBuffer if the page doesn't
* exist, and we don't check for all-zeroes. Thus, no log entry is made
@@ -424,7 +432,11 @@ XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum,
do
{
if (buffer != InvalidBuffer)
{
if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
ReleaseBuffer(buffer);
}
buffer = ReadBufferWithoutRelcache(rnode, forknum,
P_NEW, mode, NULL);
}
@@ -432,6 +444,8 @@ XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum,
/* Handle the corner case that P_NEW returns non-consecutive pages */
if (BufferGetBlockNumber(buffer) != blkno)
{
if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK)
LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
ReleaseBuffer(buffer);
buffer = ReadBufferWithoutRelcache(rnode, forknum, blkno,
mode, NULL);
@@ -537,12 +551,8 @@ RestoreBackupBlockContents(XLogRecPtr lsn, BkpBlock bkpb, char *blk,
Page page;
buffer = XLogReadBufferExtended(bkpb.node, bkpb.fork, bkpb.block,
RBM_ZERO);
get_cleanup_lock ? RBM_ZERO_AND_CLEANUP_LOCK : RBM_ZERO_AND_LOCK);
Assert(BufferIsValid(buffer));
if (get_cleanup_lock)
LockBufferForCleanup(buffer);
else
LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
page = (Page) BufferGetPage(buffer);