diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/backend/storage/lmgr/predicate.c | 26 |
1 files changed, 19 insertions, 7 deletions
diff --git a/src/backend/storage/lmgr/predicate.c b/src/backend/storage/lmgr/predicate.c index 11dede9e70b..7978bef996d 100644 --- a/src/backend/storage/lmgr/predicate.c +++ b/src/backend/storage/lmgr/predicate.c @@ -920,26 +920,38 @@ CheckPointPredicate(void) else { /* - * The SLRU is no longer needed. Truncate everything but the last - * page. We don't dare to touch the last page in case the SLRU is - * taken back to use, and the new tail falls on the same page. + * The SLRU is no longer needed. Truncate everything. If we try to + * leave the head page around to avoid re-zeroing it, we might not + * use the SLRU again until we're past the wrap-around point, which + * makes SLRU unhappy. + * + * While the API asks you to specify truncation by page, it silently + * ignores the request unless the specified page is in a segment + * past some allocated portion of the SLRU. We don't care which + * page in a later segment we hit, so just add the number of pages + * per segment to the head page to land us *somewhere* in the next + * segment. */ - tailPage = oldSerXidControl->headPage; + tailPage = oldSerXidControl->headPage + SLRU_PAGES_PER_SEGMENT; oldSerXidControl->headPage = -1; } LWLockRelease(OldSerXidLock); + /* Truncate away pages that are no longer required */ + SimpleLruTruncate(OldSerXidSlruCtl, tailPage); + /* * Flush dirty SLRU pages to disk * * This is not actually necessary from a correctness point of view. We do * it merely as a debugging aid. + * + * We're doing this after the truncation to avoid writing pages right + * before deleting the file in which they sit, which would be completely + * pointless. */ SimpleLruFlush(OldSerXidSlruCtl, true); - - /* Truncate away pages that are no longer required */ - SimpleLruTruncate(OldSerXidSlruCtl, tailPage); } /*------------------------------------------------------------------------*/ |