Horton

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

Tomas Vondra <tomas.vondra@2ndquadrant.com>

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From: Tomas Vondra <tomas.vondra@2ndquadrant.com>
To: Dilip Kumar <dilipbalaut@gmail.com>
Cc: Kuntal Ghosh <kuntalghosh.2007@gmail.com>, Amit Kapila <amit.kapila16@gmail.com>, Michael Paquier <michael@paquier.xyz>, Peter Eisentraut <peter.eisentraut@2ndquadrant.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2020-04-16T21:25:04Z
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, Apr 13, 2020 at 05:20:39PM +0530, Dilip Kumar wrote:
>On Mon, Apr 13, 2020 at 4:14 PM Kuntal Ghosh <kuntalghosh.2007@gmail.com> wrote:
>>
>> On Thu, Apr 9, 2020 at 2:40 PM Dilip Kumar <dilipbalaut@gmail.com> wrote:
>> >
>> > I have rebased the patch on the latest head.  I haven't yet changed
>> > anything for xid assignment thing because it is not yet concluded.
>> >
>> Some review comments from 0001-Immediately-WAL-log-*.patch,
>>
>> +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;
>> +
>> +}
>> IMHO, it's important to reduce the complexity of this function since
>> it's been called for every WAL insertion. During the lifespan of a
>> transaction, any of these if conditions will only be evaluated if
>> previous conditions are true. So, we can maintain some state machine
>> to avoid multiple evaluation of a condition inside a transaction. But,
>> if the overhead is not much, it's not worth I guess.
>
>Yeah maybe, in some cases we can avoid checking multiple conditions by
>maintaining that state.  But, that state will have to be at the
>transaction level.  But, I am not sure how much worth it will be to
>add one extra condition to skip a few if checks and it will also add
>the code complexity.  And, in some cases where logical decoding is not
>enabled, it may add one extra check? I mean first check the state and
>that will take you to the first if check.
>

Perhaps. I think we should only do that if we can demonstrate it's an
issue in practice. Otherwise it's just unnecessary complexity.

regards

-- 
Tomas Vondra                  http://www.2ndQuadrant.com
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