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base repository: postgresql-cfbot/postgresql
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  • 2 commits
  • 8 files changed
  • 2 contributors

Commits on Apr 29, 2025

  1. using indexscan to speedup add not null constraints 

    This patch tries to use index_beginscan() / index_getnext() / index_endscan()
mentioned in [1] to speedup adding not-null constraints to the existing table.

the main logic happen in phase3 ATRewriteTable
1. collect all not-null constraints.
2. does each not-null constraint have a corresponding index to vertify it, if
   not then do the normal processing.
3. if table scan, table rewrite, table was not in AccessExclusiveLock.
   not-null constraint was on virtual generated column
   then we can not use indexcan to fast check not-null constraint.
3. If a table scan or rewrite occurs and the table is not held with an
   AccessExclusiveLock, and the NOT NULL constraint is on a virtual generated
   column, then we can not use indexscan to fast validate not-null constraints.

concurrency concern:
ALTER TABLE SET NOT NULL will take an ACCESS EXCLUSIVE lock, so there is less
variant of racing issue can occur?  to prove accurate, I wrote some isolation
tests. see[2]

performance:
demo:
case when: %20 percent values are NULL and have been deleted from heap but they
still on the index.

drop table if exists t;
create unlogged table t(a int, b int) with (autovacuum_enabled = off, vacuum_index_cleanup=off);
insert into t select case when g % 5 = 0 then null else g end, g+1
from generate_series(1,1_000_000) g;
create index t_idx_a on t(a);
delete from t where a is null;

alter table t alter column a drop not null;
alter table t add constraint t1 not null a;

the above two statement running serval times:
patch Time:: 1.084  ms
master Time: 12.045 ms

references:
[1] https://postgr.es/m/CA%2BTgmoa5NKz8iGW_9v7wz%3D-%2BzQFu%3DE4SZoaTaU1znLaEXRYp-Q%40mail.gmail.com
[2] https://postgr.es/m/900056D1-32DF-4927-8251-3E0C0DC407FD%40anarazel.de
discussion: https://postgr.es/m/CACJufxFiW=4k1is=F1J=r-Cx1RuByXQPUrWB331U47rSnGz+hw@mail.gmail.com
commitfest entry: https://commitfest.postgresql.org/patch/5444
    @jianhe-fun
    jianhe-fun authored and Commitfest Bot committed Apr 29, 2025
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  2. [CF 5444] v5 - using index to speedup add not null constraints to a t… 

    …able

This branch was automatically generated by a robot using patches from an
email thread registered at:

https://commitfest.postgresql.org/patch/5444

The branch will be overwritten each time a new patch version is posted to
the thread, and also periodically to check for bitrot caused by changes
on the master branch.

Patch(es): https://www.postgresql.org/message-id/CACJufxHdR0Rd4-v78XhH+xNungof=zQrcTZK0GSN16zoNHWdHg@mail.gmail.com
Author(s): Jian He
    Commitfest Bot committed Apr 29, 2025
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    2d14797 View commit details
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