diff options
Diffstat (limited to 'src/backend/access/transam/xlogutils.c')
| -rw-r--r-- | src/backend/access/transam/xlogutils.c | 45 |
1 files changed, 29 insertions, 16 deletions
diff --git a/src/backend/access/transam/xlogutils.c b/src/backend/access/transam/xlogutils.c index 02b281c86ad..458af10ca19 100644 --- a/src/backend/access/transam/xlogutils.c +++ b/src/backend/access/transam/xlogutils.c @@ -11,7 +11,7 @@ * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group * Portions Copyright (c) 1994, Regents of the University of California * - * $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.66 2009/01/01 17:23:36 momjian Exp $ + * $PostgreSQL: pgsql/src/backend/access/transam/xlogutils.c,v 1.67 2009/01/20 18:59:37 heikki Exp $ * *------------------------------------------------------------------------- */ @@ -217,8 +217,19 @@ XLogCheckInvalidPages(void) /* * XLogReadBuffer - * A shorthand of XLogReadBufferExtended(), for reading from the main - * fork. + * Read a page during XLOG replay. + * + * This is a shorthand of XLogReadBufferExtended() followed by + * LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE), for reading from the main + * fork. + * + * (Getting the lock is not really necessary, since we expect that this is + * only used during single-process XLOG replay, but some subroutines such + * as MarkBufferDirty will complain if we don't. And hopefully we'll get + * hot standby support in the future, where there will be backends running + * read-only queries during XLOG replay.) + * + * 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. @@ -226,22 +237,21 @@ XLogCheckInvalidPages(void) Buffer XLogReadBuffer(RelFileNode rnode, BlockNumber blkno, bool init) { - return XLogReadBufferExtended(rnode, MAIN_FORKNUM, blkno, - init ? RBM_ZERO : RBM_NORMAL); + Buffer buf; + buf = XLogReadBufferExtended(rnode, MAIN_FORKNUM, blkno, + init ? RBM_ZERO : RBM_NORMAL); + if (BufferIsValid(buf)) + LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE); + + return buf; } /* * XLogReadBufferExtended * Read a page during XLOG replay * - * This is functionally comparable to ReadBuffer followed by - * LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE): you get back a pinned - * and locked buffer. (Getting the lock is not really necessary, since we - * expect that this is only used during single-process XLOG replay, but - * some subroutines such as MarkBufferDirty will complain if we don't.) - * - * There's some differences in the behavior wrt. the "mode" argument, - * compared to ReadBufferExtended: + * This is functionally comparable to ReadBufferExtended. There's some + * differences in the behavior wrt. the "mode" argument: * * In RBM_NORMAL mode, if the page doesn't exist, or contains all-zeroes, we * return InvalidBuffer. In this case the caller should silently skip the @@ -306,16 +316,19 @@ XLogReadBufferExtended(RelFileNode rnode, ForkNumber forknum, Assert(BufferGetBlockNumber(buffer) == blkno); } - LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE); - if (mode == RBM_NORMAL) { /* check that page has been initialized */ Page page = (Page) BufferGetPage(buffer); + /* + * We assume that PageIsNew is safe without a lock. During recovery, + * there should be no other backends that could modify the buffer at + * the same time. + */ if (PageIsNew(page)) { - UnlockReleaseBuffer(buffer); + ReleaseBuffer(buffer); log_invalid_page(rnode, forknum, blkno, true); return InvalidBuffer; } |