Re: Deferring some AtStart* allocations?

On Tue, Oct 21, 2014 at 12:00 PM, Andres Freund <andres@2ndquadrant.com> wrote:
> On 2014-10-09 15:01:19 -0400, Robert Haas wrote:
>>  /*
>> @@ -960,18 +966,38 @@ AtEOXact_Inval(bool isCommit)
> ...
>> +             /*
>> +              * We create invalidation stack entries lazily, so the parent might
>> +              * not have one.  Instead of creating one, moving all the data over,
>> +              * and then freeing our own, we can just adjust the level of our own
>> +              * entry.
>> +              */
>> +             if (myInfo->parent == NULL || myInfo->parent->my_level < my_level - 1)
>> +             {
>> +                     myInfo->my_level--;
>> +                     return;
>> +             }
>> +
>
> I think this bit might not be correct. What if the subxact one level up
> aborts? Then it'll miss dealing with these invalidation entries. Or am I
> misunderstanding something?

One of us is.  I think you're asking about a situation where we have a
transaction, and a subtransaction, and within that another
subtransaction. Only the innermost subtransaction has invalidation
messages.  At the innermost level, we commit; the above code makes
those messages the responsibility of the outer subtransaction.  If
that subtransaction abouts, AtEOSubXact_Inval() gets called again,
sees that it has messages (that it inherited from the innermost
subtransaction), and takes the exact same code-path that it would have
pre-patch.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company