Re: Multiple Xids in PGPROC?

Manfred Koizar wrote:
> With subtransactions we'd have to fall back to checking pg_clog (and
> pg_subtrans) in certain cases. There are lots of possible
> implementations. Here are some ideas (just brainstorming):
>
> . We could first scan the PGPROC array. If the xid is an active main
> transaction, we're finished.
>
> . If xid is older than RecentGlobalXmin, it cannot be active.
>
> . We could include a small number of subtransaction xids in PGPROC.
>
> . For additional subtransactions not fitting into this small array
> there could be minsubxid and maxsubxid fields in PGPROC. If the xid we
> are looking for is outside all these ranges, it cannot be an active
> subtransaction.
>
> . If all these tests fail, we fall back to checking pg_clog.

Could we add a boolean to each PROC structure indicating if that xid has
subtransactions? If none have subtransactions, we don't need to look in
pg_clog.

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