Horton

Re: [PROPOSAL] Use SnapshotAny in get_actual_variable_range

Dmitriy Sarafannikov <dsarafannikov@yandex.ru>

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From: Dmitriy Sarafannikov <dsarafannikov@yandex.ru>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: 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: 2017-04-29T08:15:25Z
Lists: pgsql-hackers 
> Maybe we need another type of snapshot that would accept any
> non-vacuumable tuple.  I really don't want SnapshotAny semantics here,
> but a tuple that was live more recently than the xmin horizon seems
> like it's acceptable enough.  HeapTupleSatisfiesVacuum already
> implements the right behavior, but we don't have a Snapshot-style
> interface for it.


If I understood correctly, this new type of snapshot would help if
there are long running transactions which can see this tuples.
But if there are not long running transactions, it will be the same.
Am i right?

And what about don’t fetch actual min and max values from indexes
whose columns doesn’t involved in join?

Commits

  1. Improve performance of get_actual_variable_range with recently-dead tuples.

  2. Use SnapshotDirty rather than an active snapshot to probe index endpoints.