Re: [PROPOSAL] Use SnapshotAny in get_actual_variable_range

Dmitriy Sarafannikov <dsarafannikov@yandex.ru>

From: Dmitriy Sarafannikov <dsarafannikov@yandex.ru>

To: Amit Kapila <amit.kapila16@gmail.com>

Cc: Tom Lane <tgl@sss.pgh.pa.us>, Robert Haas <robertmhaas@gmail.com>, "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>, Borodin Vladimir <root@simply.name>, Хомик Кирилл <khomikki@yandex-team.ru>

Date: 2017-05-08T14:23:47Z

Lists: pgsql-hackers

Attachments

snapshot_non_vacuumable_v3.patch (application/octet-stream) patch v3

> + else \
> + (snapshotdata).xmin = \
> + TransactionIdLimitedForOldSnapshots(RecentGlobalDataXmin, \
> + relation); \
> 
> I think we don't need to use TransactionIdLimitedForOldSnapshots() as
> that is required to override xmin for table vacuum/pruning purposes.
> 
>> Maybe we need
>> to use GetOldestXmin()?
> 
> It is a costly call as it needs ProcArrayLock, so I don't think it
> makes sense to use it here.

Ok, i agree. Patch is attached.

Commits

Improve performance of get_actual_variable_range with recently-dead tuples.
- 3ca930fc39cc 11.0 landed
Use SnapshotDirty rather than an active snapshot to probe index endpoints.
- fccebe421d0c 9.4.0 cited