作者
digoal
日期
2021-03-26
标签
PostgreSQL , rewrite table , 2阶段 routine , 无锁 ddl , 无锁 整理数据 , 无锁 rewrite table
背景
https://git.postgresql.org/gitweb/?p=postgresql.git;a=commit;h=cd03c6e94b09ff402cbc3ce8da5587f09f0b5e58
```
Let ALTER TABLE Phase 2 routines manage the relation pointer
author Alvaro Herrera alvherre@alvh.no-ip.org
Thu, 25 Mar 2021 18:56:11 +0000 (15:56 -0300)
committer Alvaro Herrera alvherre@alvh.no-ip.org
Thu, 25 Mar 2021 18:56:11 +0000 (15:56 -0300)
commit cd03c6e94b09ff402cbc3ce8da5587f09f0b5e58
tree 8cd6585b3e3de9c5af2c9f3305b90db47b229f40 tree
parent 4669cacbd4b4b1baa1b7f2ea53d461433a1b6276 commit | diff
Let ALTER TABLE Phase 2 routines manage the relation pointer
Struct AlteredRelationInfo gains a new Relation member, to be used only
by Phase 2 (ATRewriteCatalogs); this allows ATExecCmd() subroutines open
and close the relation internally.
A future commit will use this facility to implement an ALTER TABLE
subcommand that closes and reopens the relation across transaction
boundaries.
(It is possible to keep the relation open past phase 2 to be used by
phase 3 instead of having to reopen it that point, but there are some
minor complications with that; it's not clear that there is much to be
won from doing that, though.)
Author: Álvaro Herrera alvherre@alvh.no-ip.org
Discussion: https://postgr.es/m/20200803234854.GA24158@alvherre.pgsql
```
alter table 支持两阶段 routine 管理, 未来将基于此支持 无(短暂)锁 rewrite table(例如vacuum full, alter table rewrite table)
例如vacuum full目前需要rewrite table, 全程排他锁, 所以需要pg_repack, 而有了这个2阶段特性支持, 可以在最后切换的时候加一个ddl锁即可.
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