Add infrastructure to identify what holds back the xid horizon - #7
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Introduce GetXidHorizonBlocker() and GetXidHorizonBlockers() in procarray.c. Given an xid horizon, these search the proc array and the replication slots for what is preventing it from advancing: active transactions, idle-in-transaction sessions, prepared transactions, hot standby feedback (held either in a walsender's PGPROC or, when a physical slot is in use, in the slot itself), and logical replication slots. A blocker is described by the new XidHorizonBlocker struct, and the candidates are ranked by XidHorizonBlockerType so that the single highest-priority (root-cause) blocker can be reported. A companion GetPreparedTransactionGid() in twophase.c resolves the GID of a blocking prepared transaction. This is infrastructure with no in-tree caller yet. A following patch uses it to report the blocker in VACUUM's log output, and the same API can underpin a future SQL-callable view that lists every blocker. Author: Shinya Kato <shinya11.kato@gmail.com> Reviewed-by: wenhui qiu <qiuwenhuifx@gmail.com> Reviewed-by: Fujii Masao <masao.fujii@gmail.com> Reviewed-by: Sami Imseih <samimseih@gmail.com> Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com> Reviewed-by: Japin Li <japinli@hotmail.com> Discussion: https://postgr.es/m/CAOzEurSgy-gDtwFmEbj5+R9PL0_G3qYB6nnzJtNStyuf87VSVg@mail.gmail.com
When VACUUM encounters recently-dead tuples that cannot be removed, it is often unclear what is preventing the xid horizon from advancing. Using the infrastructure added in the previous patch, VACUUM (VERBOSE) and log_autovacuum output now report the highest-priority blocker that is holding back OldestXmin, with identifying details: the backend pid, the prepared transaction GID, the standby application_name, or the replication slot name. Because the horizon was computed earlier, the result is best-effort: the original blocker may have already committed by the time it is looked up, in which case a different blocker or none at all may be reported. Author: Shinya Kato <shinya11.kato@gmail.com> Reviewed-by: wenhui qiu <qiuwenhuifx@gmail.com> Reviewed-by: Fujii Masao <masao.fujii@gmail.com> Reviewed-by: Sami Imseih <samimseih@gmail.com> Reviewed-by: Dilip Kumar <dilipbalaut@gmail.com> Reviewed-by: Japin Li <japinli@hotmail.com> Discussion: https://postgr.es/m/CAOzEurSgy-gDtwFmEbj5+R9PL0_G3qYB6nnzJtNStyuf87VSVg@mail.gmail.com
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Introduce GetXidHorizonBlocker() and GetXidHorizonBlockers() in
procarray.c. Given an xid horizon, these search the proc array and the
replication slots for what is preventing it from advancing: active
transactions, idle-in-transaction sessions, prepared transactions, hot
standby feedback (held either in a walsender's PGPROC or, when a physical
slot is in use, in the slot itself), and logical replication slots.
A blocker is described by the new XidHorizonBlocker struct, and the
candidates are ranked by XidHorizonBlockerType so that the single
highest-priority (root-cause) blocker can be reported. A companion
GetPreparedTransactionGid() in twophase.c resolves the GID of a blocking
prepared transaction.
This is infrastructure with no in-tree caller yet. A following patch
uses it to report the blocker in VACUUM's log output, and the same API
can underpin a future SQL-callable view that lists every blocker.
Author: Shinya Kato shinya11.kato@gmail.com
Reviewed-by: wenhui qiu qiuwenhuifx@gmail.com
Reviewed-by: Fujii Masao masao.fujii@gmail.com
Reviewed-by: Sami Imseih samimseih@gmail.com
Reviewed-by: Dilip Kumar dilipbalaut@gmail.com
Reviewed-by: Japin Li japinli@hotmail.com
Discussion: https://postgr.es/m/CAOzEurSgy-gDtwFmEbj5+R9PL0_G3qYB6nnzJtNStyuf87VSVg@mail.gmail.com