diff options
Diffstat (limited to 'src/backend/storage/buffer/bufmgr.c')
| -rw-r--r-- | src/backend/storage/buffer/bufmgr.c | 41 |
1 files changed, 37 insertions, 4 deletions
diff --git a/src/backend/storage/buffer/bufmgr.c b/src/backend/storage/buffer/bufmgr.c index cbfe05e2b5c..9b62aecd917 100644 --- a/src/backend/storage/buffer/bufmgr.c +++ b/src/backend/storage/buffer/bufmgr.c @@ -499,14 +499,19 @@ ReadBuffer(Relation reln, BlockNumber blockNum) * valid, the page is zeroed instead of throwing an error. This is intended * for non-critical data, where the caller is prepared to repair errors. * - * In RBM_ZERO mode, if the page isn't in buffer cache already, it's filled - * with zeros instead of reading it from disk. Useful when the caller is - * going to fill the page from scratch, since this saves I/O and avoids + * In RBM_ZERO_AND_LOCK mode, if the page isn't in buffer cache already, it's + * filled with zeros instead of reading it from disk. Useful when the caller + * is going to fill the page from scratch, since this saves I/O and avoids * unnecessary failure if the page-on-disk has corrupt page headers. + * The page is returned locked to ensure that the caller has a chance to + * initialize the page before it's made visible to others. * Caution: do not use this mode to read a page that is beyond the relation's * current physical EOF; that is likely to cause problems in md.c when * the page is modified and written out. P_NEW is OK, though. * + * RBM_ZERO_AND_CLEANUP_LOCK is the same as RBM_ZERO_AND_LOCK, but acquires + * a cleanup-strength lock on the page. + * * RBM_NORMAL_NO_LOG mode is treated the same as RBM_NORMAL here. * * If strategy is not NULL, a nondefault buffer access strategy is used. @@ -648,6 +653,18 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, isExtend, found); + /* + * In RBM_ZERO_AND_LOCK mode the caller expects the page to + * be locked on return. + */ + if (!isLocalBuf) + { + if (mode == RBM_ZERO_AND_LOCK) + LWLockAcquire(bufHdr->content_lock, LW_EXCLUSIVE); + else if (mode == RBM_ZERO_AND_CLEANUP_LOCK) + LockBufferForCleanup(BufferDescriptorGetBuffer(bufHdr)); + } + return BufferDescriptorGetBuffer(bufHdr); } @@ -729,7 +746,7 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, * Read in the page, unless the caller intends to overwrite it and * just wants us to allocate a buffer. */ - if (mode == RBM_ZERO) + if (mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK) MemSet((char *) bufBlock, 0, BLCKSZ); else { @@ -771,6 +788,22 @@ ReadBuffer_common(SMgrRelation smgr, char relpersistence, ForkNumber forkNum, } } + /* + * In RBM_ZERO_AND_LOCK mode, grab the buffer content lock before marking + * the page as valid, to make sure that no other backend sees the zeroed + * page before the caller has had a chance to initialize it. + * + * Since no-one else can be looking at the page contents yet, there is no + * difference between an exclusive lock and a cleanup-strength lock. + * (Note that we cannot use LockBuffer() of LockBufferForCleanup() here, + * because they assert that the buffer is already valid.) + */ + if ((mode == RBM_ZERO_AND_LOCK || mode == RBM_ZERO_AND_CLEANUP_LOCK) && + !isLocalBuf) + { + LWLockAcquire(bufHdr->content_lock, LW_EXCLUSIVE); + } + if (isLocalBuf) { /* Only need to adjust flags */ |