diff options
Diffstat (limited to 'src/backend/storage/ipc/standby.c')
| -rw-r--r-- | src/backend/storage/ipc/standby.c | 30 |
1 files changed, 29 insertions, 1 deletions
diff --git a/src/backend/storage/ipc/standby.c b/src/backend/storage/ipc/standby.c index fb5f18edfc7..aa8bea5538b 100644 --- a/src/backend/storage/ipc/standby.c +++ b/src/backend/storage/ipc/standby.c @@ -800,7 +800,9 @@ standby_redo(XLogRecPtr lsn, XLogRecord *record) /* * Log details of the current snapshot to WAL. This allows the snapshot state - * to be reconstructed on the standby. + * to be reconstructed on the standby and for logical decoding. + * + * This is used for Hot Standby as follows: * * We can move directly to STANDBY_SNAPSHOT_READY at startup if we * start from a shutdown checkpoint because we know nothing was running @@ -854,6 +856,12 @@ standby_redo(XLogRecPtr lsn, XLogRecord *record) * Zero xids should no longer be possible, but we may be replaying WAL * from a time when they were possible. * + * For logical decoding only the running xacts information is needed; + * there's no need to look at the locking information, but it's logged anyway, + * as there's no independent knob to just enable logical decoding. For + * details of how this is used, check snapbuild.c's introductory comment. + * + * * Returns the RecPtr of the last inserted record. */ XLogRecPtr @@ -879,8 +887,28 @@ LogStandbySnapshot(void) * record we write, because standby will open up when it sees this. */ running = GetRunningTransactionData(); + + /* + * GetRunningTransactionData() acquired ProcArrayLock, we must release + * it. For Hot Standby this can be done before inserting the WAL record + * because ProcArrayApplyRecoveryInfo() rechecks the commit status using + * the clog. For logical decoding, though, the lock can't be released + * early becuase the clog might be "in the future" from the POV of the + * historic snapshot. This would allow for situations where we're waiting + * for the end of a transaction listed in the xl_running_xacts record + * which, according to the WAL, have commit before the xl_running_xacts + * record. Fortunately this routine isn't executed frequently, and it's + * only a shared lock. + */ + if (wal_level < WAL_LEVEL_LOGICAL) + LWLockRelease(ProcArrayLock); + recptr = LogCurrentRunningXacts(running); + /* Release lock if we kept it longer ... */ + if (wal_level >= WAL_LEVEL_LOGICAL) + LWLockRelease(ProcArrayLock); + /* GetRunningTransactionData() acquired XidGenLock, we must release it */ LWLockRelease(XidGenLock); |