Re: New Event Trigger: table_rewrite

On Tue, Nov 18, 2014 at 5:14 PM, Dimitri Fontaine
<dimitri(at)2ndquadrant(dot)fr> wrote:
> Robert Haas <robertmhaas(at)gmail(dot)com> writes:
>> It seems pretty weird, also, that the event trigger will fire after
>> we've taken AccessExclusiveLock when you cluster a particular
>> relation, and before we've taken AccessExclusiveLock when you cluster
>> database-wide. That's more or less an implementation artifact of the
>> current code that we're exposing to the use for, really, no good
>> reason.
>
> In the CLUSTER implementation we have only one call site for invoking
> the Event Trigger, in cluster_rel(). While it's true that in the single
> relation case, the relation is opened in cluster() then cluster_rel() is
> called, the opening is done with NoLock in cluster():
>
> rel = heap_open(tableOid, NoLock);
>
> My understanding is that the relation locking only happens in
> cluster_rel() at this line:
>
> OldHeap = try_relation_open(tableOid, AccessExclusiveLock);
>
> Please help me through the cluster locking strategy here, I feel like
> I'm missing something obvious, as my conclusion from re-reading the code
> in lights of your comment is that your comment is not accurate with
> respect to the current state of the code.

Unless I'm missing something, when you cluster a particular relation,
cluster() does this:

/* Find and lock the table */
rel = heap_openrv(stmt->relation, AccessExclusiveLock);

I don't see the "rel = heap_open(tableOid, NoLock);" line you quoted anywhere.

--
Robert Haas
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