Horton

Re: Remove HeapTuple and Buffer dependency for predicate locking functions

Andres Freund <andres@anarazel.de>

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From: Andres Freund <andres@anarazel.de>
To: Ashwin Agrawal <aagrawal@pivotal.io>
Cc: Thomas Munro <thomas.munro@gmail.com>, PostgreSQL mailing lists <pgsql-hackers@postgresql.org>, Kuntal Ghosh <kuntalghosh.2007@gmail.com>
Date: 2019-07-31T17:55:48Z
Lists: pgsql-hackers 
Hi,

On 2019-07-31 10:42:50 -0700, Ashwin Agrawal wrote:
> On Tue, Jul 30, 2019 at 2:58 PM Thomas Munro <thomas.munro@gmail.com> wrote:
> 
> > On Tue, Jun 25, 2019 at 6:02 AM Andres Freund <andres@anarazel.de> wrote:
> > > > - CheckForSerializableConflictOut() no more takes HeapTuple nor
> > > >   buffer, instead just takes xid. Push heap specific parts from
> > > >   CheckForSerializableConflictOut() into its own function
> > > >   HeapCheckForSerializableConflictOut() which calls
> > > >   CheckForSerializableConflictOut(). The alternative option could be
> > > >   CheckForSerializableConflictOut() take callback function and
> > > >   callback arguments, which gets called if required after performing
> > > >   prechecks. Though currently I fell AM having its own wrapper to
> > > >   perform AM specific task and then calling
> > > >   CheckForSerializableConflictOut() is fine.
> > >
> > > I think it's right to move the xid handling out of
> > > CheckForSerializableConflictOut(). But I think we also ought to move the
> > > subtransaction handling out of the function - e.g. zheap doesn't
> > > want/need that.
> >
> > Thoughts on this Ashwin?
> >
> 
> I think the only part its doing for sub-transaction is
> SubTransGetTopmostTransaction(xid). If xid passed to this function is
> already top most transaction which is case for zheap and zedstore, then
> there is no downside to keeping that code here in common place.

Well, it's far from a cheap function. It'll do unnecessary on-disk
lookups in many cases. I'd call that quite a downside.

Greetings,

Andres Freund

Commits

  1. Remove dependency on HeapTuple from predicate locking functions.

  2. Optimize PredicateLockTuple().

  3. Optimize TransactionIdIsCurrentTransactionId().

  4. Fix predicate-locking of HOT updated rows.

  5. Introduce logical decoding.

  6. Fix bugs in SSI tuple locking.

  7. Implement genuine serializable isolation level.