diff options
Diffstat (limited to 'src/backend/access/transam/multixact.c')
| -rw-r--r-- | src/backend/access/transam/multixact.c | 38 |
1 files changed, 24 insertions, 14 deletions
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c index ce84dac0c40..ff960833f95 100644 --- a/src/backend/access/transam/multixact.c +++ b/src/backend/access/transam/multixact.c @@ -1832,10 +1832,12 @@ MultiXactShmemInit(void) "MultiXactOffset", NUM_MULTIXACTOFFSET_BUFFERS, 0, MultiXactOffsetSLRULock, "pg_multixact/offsets", LWTRANCHE_MULTIXACTOFFSET_BUFFER); + SlruPagePrecedesUnitTests(MultiXactOffsetCtl, MULTIXACT_OFFSETS_PER_PAGE); SimpleLruInit(MultiXactMemberCtl, "MultiXactMember", NUM_MULTIXACTMEMBER_BUFFERS, 0, MultiXactMemberSLRULock, "pg_multixact/members", LWTRANCHE_MULTIXACTMEMBER_BUFFER); + /* doesn't call SimpleLruTruncate() or meet criteria for unit tests */ /* Initialize our shared state struct */ MultiXactState = ShmemInitStruct("Shared MultiXact State", @@ -2978,6 +2980,14 @@ TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB) * truncate the members SLRU. So we first scan the directory to determine * the earliest offsets page number that we can read without error. * + * When nextMXact is less than one segment away from multiWrapLimit, + * SlruScanDirCbFindEarliest can find some early segment other than the + * actual earliest. (MultiXactOffsetPagePrecedes(EARLIEST, LATEST) + * returns false, because not all pairs of entries have the same answer.) + * That can also arise when an earlier truncation attempt failed unlink() + * or returned early from this function. The only consequence is + * returning early, which wastes space that we could have liberated. + * * NB: It's also possible that the page that oldestMulti is on has already * been truncated away, and we crashed before updating oldestMulti. */ @@ -3092,15 +3102,11 @@ TruncateMultiXact(MultiXactId newOldestMulti, Oid newOldestMultiDB) } /* - * Decide which of two MultiXactOffset page numbers is "older" for truncation - * purposes. - * - * We need to use comparison of MultiXactId here in order to do the right - * thing with wraparound. However, if we are asked about page number zero, we - * don't want to hand InvalidMultiXactId to MultiXactIdPrecedes: it'll get - * weird. So, offset both multis by FirstMultiXactId to avoid that. - * (Actually, the current implementation doesn't do anything weird with - * InvalidMultiXactId, but there's no harm in leaving this code like this.) + * Decide whether a MultiXactOffset page number is "older" for truncation + * purposes. Analogous to CLOGPagePrecedes(). + * + * Offsetting the values is optional, because MultiXactIdPrecedes() has + * translational symmetry. */ static bool MultiXactOffsetPagePrecedes(int page1, int page2) @@ -3109,15 +3115,17 @@ MultiXactOffsetPagePrecedes(int page1, int page2) MultiXactId multi2; multi1 = ((MultiXactId) page1) * MULTIXACT_OFFSETS_PER_PAGE; - multi1 += FirstMultiXactId; + multi1 += FirstMultiXactId + 1; multi2 = ((MultiXactId) page2) * MULTIXACT_OFFSETS_PER_PAGE; - multi2 += FirstMultiXactId; + multi2 += FirstMultiXactId + 1; - return MultiXactIdPrecedes(multi1, multi2); + return (MultiXactIdPrecedes(multi1, multi2) && + MultiXactIdPrecedes(multi1, + multi2 + MULTIXACT_OFFSETS_PER_PAGE - 1)); } /* - * Decide which of two MultiXactMember page numbers is "older" for truncation + * Decide whether a MultiXactMember page number is "older" for truncation * purposes. There is no "invalid offset number" so use the numbers verbatim. */ static bool @@ -3129,7 +3137,9 @@ MultiXactMemberPagePrecedes(int page1, int page2) offset1 = ((MultiXactOffset) page1) * MULTIXACT_MEMBERS_PER_PAGE; offset2 = ((MultiXactOffset) page2) * MULTIXACT_MEMBERS_PER_PAGE; - return MultiXactOffsetPrecedes(offset1, offset2); + return (MultiXactOffsetPrecedes(offset1, offset2) && + MultiXactOffsetPrecedes(offset1, + offset2 + MULTIXACT_MEMBERS_PER_PAGE - 1)); } /* |