Horton

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

Dilip Kumar <dilipbalaut@gmail.com>

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From: Dilip Kumar <dilipbalaut@gmail.com>
To: Tomas Vondra <tomas.vondra@2ndquadrant.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, Michael Paquier <michael@paquier.xyz>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-03-04T03:43:49Z
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 Wed, Mar 4, 2020 at 3:16 AM Tomas Vondra
<tomas.vondra@2ndquadrant.com> wrote:
>
> Hi,
>
> I started looking at this patch series again, hoping to get it moving
> for PG13.

Nice.

 There's been a tremendous amount of work done since I last
> worked on it, and a lot was discussed on this thread, so it'll take a
> while to get familiar with the new code ...
>
> The first thing I realized that WAL-logging of assignments in v12 does
> both the "old" logging (using dedicated message) and "new" with
> toplevel-XID embedded in the first message. Yes, the patch was wrong,
> because it eliminated all calls to ProcArrayApplyXidAssignment() and so
> it was trivial to crash the replica due to KnownAssignedXids overflow.
> But I don't think re-introducing XLOG_XACT_ASSIGNMENT message is the
> right fix.
>
> I actually proposed doing this (having both ways to log assignments) so
> that there's no regression risk with (wal_level < logical). But IIRC
> Andres objected to it, argumenting that we should not log the same piece
> of information in two very different ways at the same time (IIRC it was
> discussed on the FOSDEM dev meeting, so I don't have a link to share).
> And I do agree with him ...
>
> The question is, why couldn't the replica use the same assignment info
> we already write for logical decoding? The main challenge is that now
> the assignment can be sent in many different xlog messages, from a bunch
> of resource managers (essentially, any xlog message with a xid can have
> embedded XID of the toplevel xact). So the handling would either need to
> happen in every rmgr, or we need to move it before we call the rmgr.
>
> For exampple, we might do this e.g. in StartupXLOG() I think, per the
> attached patch (FWIW this particular fix was written by Masahiko Sawada,
> not me). This does the trick for me - I'm no longer able to reproduce
> the KnownAssignedXids overflow.
>
> The one difference is that we used to call ProcArrayApplyXidAssignment
> for larger groups of XIDs, as sent in the assignment message. Now we
> call it for each individual assignment. I don't know if this is an
> issue, but I suppose we might introduce some sort of local caching
> (accumulate the assignments into a local array, call the function only
> when we have enough of them).

Thanks for the pointers,  I will think over these points.

>
> Aside from that, I think there's a minor bug in xact.c - the patch adds
> a "assigned" field to TransactionStateData, but then it fails to add a
> default value into TopTransactionStateData. We probably interpret NULL
> as false, but then there's nothing for the pointer. I suspect it might
> leave some random garbage there, leading to strange things later.

Actually, we will never access that field for the
TopTransactionStateData, right?
See below code,  we have a check that only if IsSubTransaction(), then
we access the "assigned" filed.

+bool
+IsSubTransactionAssignmentPending(void)
+{
+ if (!XLogLogicalInfoActive())
+ return false;
+
+ /* we need to be in a transaction state */
+ if (!IsTransactionState())
+ return false;
+
+ /* it has to be a subtransaction */
+ if (!IsSubTransaction())
+ return false;
+
+ /* the subtransaction has to have a XID assigned */
+ if (!TransactionIdIsValid(GetCurrentTransactionIdIfAny()))
+ return false;
+
+ /* and it needs to have 'assigned' */
+ return !CurrentTransactionState->assigned;
+
+}

>
> Another thing I noticed is LogicalDecodingProcessRecord() extracts the
> toplevel XID using a macro
>
>    txid = XLogRecGetTopXid(record);
>
> but then it just starts accessing the fields directly again in the
> ReorderBufferAssignChild call. I think we should do this instead:
>
>      ReorderBufferAssignChild(ctx->reorder,
>                               txid,
>                              XLogRecGetXid(record),
>                               buf.origptr);

Make sense.  I will change this in the patch.

-- 
Regards,
Dilip Kumar
EnterpriseDB: http://www.enterprisedb.com