diff options
Diffstat (limited to 'src/backend/access/transam/multixact.c')
| -rw-r--r-- | src/backend/access/transam/multixact.c | 21 |
1 files changed, 12 insertions, 9 deletions
diff --git a/src/backend/access/transam/multixact.c b/src/backend/access/transam/multixact.c index 93824653376..d4ad6787a59 100644 --- a/src/backend/access/transam/multixact.c +++ b/src/backend/access/transam/multixact.c @@ -2055,11 +2055,13 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid) Assert(MultiXactIdIsValid(oldest_datminmxid)); /* - * The place where we actually get into deep trouble is halfway around - * from the oldest potentially-existing XID/multi. (This calculation is - * probably off by one or two counts for Xids, because the special XIDs - * reduce the size of the loop a little bit. But we throw in plenty of - * slop below, so it doesn't matter.) + * Since multixacts wrap differently from transaction IDs, this logic is + * not entirely correct: in some scenarios we could go for longer than 2 + * billion multixacts without seeing any data loss, and in some others we + * could get in trouble before that if the new pg_multixact/members data + * stomps on the previous cycle's data. For lack of a better mechanism we + * use the same logic as for transaction IDs, that is, start taking action + * halfway around the oldest potentially-existing multixact. */ multiWrapLimit = oldest_datminmxid + (MaxMultiXactId >> 1); if (multiWrapLimit < FirstMultiXactId) @@ -2093,12 +2095,13 @@ SetMultiXactIdLimit(MultiXactId oldest_datminmxid, Oid oldest_datoid) /* * We'll start trying to force autovacuums when oldest_datminmxid gets to - * be more than autovacuum_freeze_max_age mxids old. + * be more than autovacuum_multixact_freeze_max_age mxids old. * - * It's a bit ugly to just reuse limits for xids that way, but it doesn't - * seem worth adding separate GUCs for that purpose. + * Note: autovacuum_multixact_freeze_max_age is a PGC_POSTMASTER parameter + * so that we don't have to worry about dealing with on-the-fly changes in + * its value. See SetTransactionIdLimit. */ - multiVacLimit = oldest_datminmxid + autovacuum_freeze_max_age; + multiVacLimit = oldest_datminmxid + autovacuum_multixact_freeze_max_age; if (multiVacLimit < FirstMultiXactId) multiVacLimit += FirstMultiXactId; |