From: | Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com> |
---|---|
To: | Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov> |
Cc: | pgsql-hackers(at)postgresql(dot)org |
Subject: | Re: SSI patch version 14 |
Date: | 2011-01-26 07:20:39 |
Message-ID: | 4D3FCB47.6060805@enterprisedb.com |
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Lists: | pgsql-hackers |
On 25.01.2011 22:53, Kevin Grittner wrote:
> Heikki Linnakangas<heikki(dot)linnakangas(at)enterprisedb(dot)com> wrote:
>> On 25.01.2011 05:30, Kevin Grittner wrote:
>
>> The readme says this:
>>> 4. PostgreSQL supports subtransactions -- an issue not mentioned
>>> in the papers.
>>
>> But I don't see any mention anywhere else on how subtransactions
>> are handled. If a subtransaction aborts, are its predicate locks
>> immediately released?
>
> No. Here's the reasoning. Within a top level transaction, you
> might start a subtransaction, read some data, and then decide based
> on what you read that the subtransaction should be rolled back. If
> the decision as to what is part of the top level transaction can
> depend on what is read in the subtransaction, predicate locks taken
> by the subtransaction must survive rollback of the subtransaction.
>
> Does that make sense to you?
Yes, that's what I suspected. And I gather that all the data structures
in predicate.c work with top-level xids, not subxids. When looking at an
xid that comes from a tuple's xmin or xmax, for example, you always call
SubTransGetTopmostTransaction() before doing much else with it.
> Is there somewhere you would like to
> see that argument documented?
README-SSI .
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
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