| From: | Sergei Kornilov <sk(at)zsrv(dot)org> |
|---|---|
| To: | Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>, Kyotaro HORIGUCHI <horiguchi(dot)kyotaro(at)lab(dot)ntt(dot)co(dot)jp> |
| Cc: | Haribabu Kommi <kommi(dot)haribabu(at)gmail(dot)com>, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Michael Paquier <michael(dot)paquier(at)gmail(dot)com>, Amit Langote <langote_amit_f8(at)lab(dot)ntt(dot)co(dot)jp>, Thomas Munro <thomas(dot)munro(at)enterprisedb(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, Claudio Freire <klaussfreire(at)gmail(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Pavan Deolasee <pavan(dot)deolasee(at)gmail(dot)com>, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] Block level parallel vacuum |
| Date: | 2019-03-21 11:04:59 |
| Message-ID: | 4963141553166299@myt3-c7e5d17fe013.qloud-c.yandex.net |
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| Lists: | pgsql-hackers |
Hello
> * in_parallel is true if we're performing parallel lazy vacuum. Since any
> * updates are not allowed during parallel mode we don't update statistics
> * but set the index bulk-deletion result to *stats. Otherwise we update it
> * and set NULL.
lazy_cleanup_index has in_parallel argument only for this purpose, but caller still should check in_parallel after lazy_cleanup_index call and do something else with stats for parallel execution.
Would be better always return stats and update statistics in caller? It's possible to update all index stats in lazy_vacuum_all_indexes for example? This routine is always parallel leader and has comment /* Do post-vacuum cleanup and statistics update for each index */ on for_cleanup=true call.
I think we need note in documentation that parallel leader is not counted in PARALLEL N option, so with PARALLEL 2 option we want use 3 processes. Or even change behavior? Default with PARALLEL 1 - only current backend in single process is running, PARALLEL 2 - leader + one parallel worker, two processes works in parallel.
regards, Sergei
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