Horton

Re: PATCH: logical_work_mem and logical streaming of large in-progress transactions

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Tomas Vondra <tomas.vondra@2ndquadrant.com>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2019-10-21T09:20:14Z
Lists: pgsql-hackers

Commits

Same data as JSON: GET /api/v1/messages/:b64id/commits the thread's linked commits as JSON, with link sources. API reference →

  1. Tighten the concurrent abort check during decoding.

  2. Improve hash_create()'s API for some added robustness.

  3. Use HASH_BLOBS for xidhash.

  4. Fix initialization of RelationSyncEntry for streaming transactions.

  5. Remove unused function declaration in logicalproto.h.

  6. Add additional tests to test streaming of in-progress transactions.

  7. Fix inline marking introduced in commit 464824323e.

  8. Add support for streaming to built-in logical replication.

  9. Fix the SharedFileSetUnregister API.

  10. Fix comment in procarray.c

  11. Suppress compiler warning in non-cassert builds.

  12. Extend the BufFile interface.

  13. Mark a few logical decoding related variables with PGDLLIMPORT.

  14. Implement streaming mode in ReorderBuffer.

  15. Extend the logical decoding output plugin API with stream methods.

  16. WAL Log invalidations at command end with wal_level=logical.

  17. Immediately WAL-log subtransaction and top-level XID association.

  18. Allow logical replication to transfer data in binary format.

  19. Only superuser can set sslcert/sslkey in postgres_fdw user mappings

  20. Track statistics for spilling of changes from ReorderBuffer.

  21. Add logical_decoding_work_mem to limit ReorderBuffer memory usage.

  22. logical decoding: process ASSIGNMENT during snapshot build

  23. Emit invalidations to standby for transactions without xid.

On Mon, Oct 21, 2019 at 10:48 AM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>
> On Fri, Oct 18, 2019 at 5:32 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
>
> > 3.
> > @@ -2479,7 +2480,7 @@ ReorderBufferSerializeTXN(ReorderBuffer *rb,
> > ReorderBufferTXN *txn)
> >
> >   /* update the statistics */
> >   rb->spillCount += 1;
> > - rb->spillTxns += txn->serialized ? 1 : 0;
> > + rb->spillTxns += txn->serialized ? 0 : 1;
> >   rb->spillBytes += size;
> >
> > Why is this change required?  Shouldn't we increase the spillTxns
> > count only when the txn is serialized?
>
> Prior to this change it was increasing the rb->spillTxns, every time
> we try to serialize the changes of the transaction.  Now, only we
> increase first time when it is not yet serialized.
>
> >
> > 3.
> > ReorderBufferSerializeTXN()
> > {
> > ..
> > /* update the statistics */
> > rb->spillCount += 1;
> > rb->spillTxns += txn->serialized ? 0 : 1;
> > rb->spillBytes += size;
> >
> > Assert(spilled == txn->nentries_mem);
> > Assert(dlist_is_empty(&txn->changes));
> > txn->nentries_mem = 0;
> > txn->serialized = true;
> > ..
> > }
> >
> > I am not able to understand the above code.  We are setting the
> > serialized parameter a few lines after we check it and increment the
> > spillTxns count. Can you please explain it?
>
> Basically, when the first time we attempt to serialize a transaction,
> txn->serialized will be false, that time we will increment the
> rb->spillTxns and after that set txn->serialized to true.  From next
> time onwards if we try to serialize the same transaction we will not
> increment the rb->spillTxns so that we count each transaction only
> once.
>

Your explanation for both the above comments makes sense to me.  Can
you please add some comments along these lines because it is not
apparent why one wants to increase the spillTxns counter when
txn->serialized is false?

> >
> > Also, isn't spillTxns count bit confusing, because in some cases it
> > will include subtransactions and other cases (where the largest picked
> > transaction is a subtransaction) it won't include it?
>
> I did not understand your comment completely.  Basically,  every
> transaction which we are serializing we will increase the count first
> time right? whether it is the main transaction or the sub-transaction.
>

It was not clear to me earlier whether we always increase the
spillTxns counter for subtransactions or not.  But now, looking at
code carefully, it is clear that is it is getting increased in every
case.  In short, you don't need to do anything for this comment.

-- 
With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com