Hi all, I've get found out that issue in my project. Update in PRIMARY while pg_basebackup is performing, Can cause the STANDBY could not UPDATE after promote.
In Standby Node, when first XID of a page come, pg_subtrans must be extended by ExtendSUBTRANS function. But if that XID created while pg_basebackup (with "-x" option) was performing, it did not extend. Due to that, after basebackup complete, start that DB and do promote complete. It failed in SAVEPOINT UPDATE query like follows. --- postgres=# BEGIN; postgres=# SAVEPOINT testsavepoint; postgres=# UPDATE test_tbl SET name = 'test'; ERROR: could not access status of transaction 1409172 DETAIL: Could not read from file "pg_subtrans/0015" at offset 131072: Success. --- I've also confirm source and realize that, When StartupXLOG call RecordKnownAssignedTransactionIds (in the "main redo apply loop"), the "standbyState" still was STANDBY_INITIALIZED, so it is returned without goto ExtendSUBTRANS (to check and extend space for pg_subtrans). Therefor, after STANDBY promote, when UPDATE query made by SAVEPOINT is executed, the process as follow is performed and get the above ERROR in SimpleLruReadPage function. AssignTransactionId => SubTransSetParent => SubTransSetParent => SimpleLruReadPage I think that ExtendSUBTRANS must be called even if "standbyState" in STANDBY_INITIALIZED in order to avoid the case above. I also attach a patch. Could anyone confirm for me. Regard, --- Dang Minh Huong NEC Soft,Ltd. http://www.necsoft.com/eng/
subtrans.patch
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