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

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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

6
src/backend/access/heap/heapam.c
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@ -7556,7 +7556,7 @@ heap_xlog_insert(XLogRecPtr lsn, XLogRecord *record)
{
XLogReadBufferForRedoExtended(lsn, record, 0,
target_node, MAIN_FORKNUM, blkno,
RBM_ZERO, false, &buffer);
RBM_ZERO_AND_LOCK, false, &buffer);
page = BufferGetPage(buffer);
PageInit(page, BufferGetPageSize(buffer), 0);
action = BLK_NEEDS_REDO;
@ -7683,7 +7683,7 @@ heap_xlog_multi_insert(XLogRecPtr lsn, XLogRecord *record)
{
XLogReadBufferForRedoExtended(lsn, record, 0,
rnode, MAIN_FORKNUM, blkno,
RBM_ZERO, false, &buffer);
RBM_ZERO_AND_LOCK, false, &buffer);
page = BufferGetPage(buffer);
PageInit(page, BufferGetPageSize(buffer), 0);
action = BLK_NEEDS_REDO;
@ -7876,7 +7876,7 @@ heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool hot_update)
{
XLogReadBufferForRedoExtended(lsn, record, 1,
rnode, MAIN_FORKNUM, newblk,
RBM_ZERO, false, &nbuffer);
RBM_ZERO_AND_LOCK, false, &nbuffer);
page = (Page) BufferGetPage(nbuffer);
PageInit(page, BufferGetPageSize(nbuffer), 0);
newaction = BLK_NEEDS_REDO;