Horton

Re: Skipping logical replication transactions on subscriber side

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: "houzj.fnst@fujitsu.com" <houzj.fnst@fujitsu.com>, "tanghy.fnst@fujitsu.com" <tanghy.fnst@fujitsu.com>, "osumi.takamichi@fujitsu.com" <osumi.takamichi@fujitsu.com>, Alexey Lesovsky <lesovsky@gmail.com>, Peter Eisentraut <peter.eisentraut@enterprisedb.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Greg Nancarrow <gregn4422@gmail.com>
Date: 2021-09-27T03:24:26Z
Lists: pgsql-hackers 
On Mon, Sep 27, 2021 at 6:21 AM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>
> On Sat, Sep 25, 2021 at 4:23 PM Amit Kapila <amit.kapila16@gmail.com> wrote:
> >
> > Sure, but each tablesync worker must have a separate relid. Why can't
> > we have a single hash table for both apply and table sync workers
> > which are hashed by sub_id + rel_id? For apply worker, the rel_id will
> > always be zero (InvalidOId) and tablesync workers will have a unique
> > OID for rel_id, so we should be able to uniquely identify each of
> > apply and table sync workers.
>
> What I imagined is to extend the subscription statistics, for
> instance, transaction stats[1]. By having a hash table for
> subscriptions, we can store those statistics into an entry of the hash
> table and we can think of subscription errors as also statistics of
> the subscription. So we can have another hash table for errors in an
> entry of the subscription hash table. For example, the subscription
> entry struct will be something like:
>
> typedef struct PgStat_StatSubEntry
> {
>     Oid subid; /* hash key */
>
>     HTAB *errors;    /* apply and table sync errors */
>
>     /* transaction stats of subscription */
>     PgStat_Counter xact_commit;
>     PgStat_Counter xact_commit_bytes;
>     PgStat_Counter xact_error;
>     PgStat_Counter xact_error_bytes;
>     PgStat_Counter xact_abort;
>     PgStat_Counter xact_abort_bytes;
>     PgStat_Counter failure_count;
> } PgStat_StatSubEntry;
>

I think these additional stats will be displayed via
pg_stat_subscription, right? If so, the current stats of that view are
all in-memory and are per LogicalRepWorker which means that for those
stats also we will have different entries for apply and table sync
worker. If this understanding is correct, won't it be better to
represent this as below?

typedef struct PgStat_StatSubWorkerEntry
{
    /* hash key */
   Oid subid;
   Oid relid

  /* worker stats which includes xact stats */
  PgStat_SubWorkerStats worker_stats

  /* error stats */
  PgStat_StatSubErrEntry worker_error_stats;
} PgStat_StatSubWorkerEntry;


typedef struct PgStat_SubWorkerStats
{
    /* define existing stats here */
....

    /* transaction stats of subscription */
    PgStat_Counter xact_commit;
    PgStat_Counter xact_commit_bytes;
    PgStat_Counter xact_error;
    PgStat_Counter xact_error_bytes;
    PgStat_Counter xact_abort;
    PgStat_Counter xact_abort_bytes;
} PgStat_SubWorkerStats;

Now, at drop subscription, we do need to find and remove all the subid
+ relid entries.

-- 
With Regards,
Amit Kapila.

Commits

  1. Test ALIGNOF_DOUBLE==4 compatibility under ALIGNOF_DOUBLE==8.

  2. Reorder subskiplsn in pg_subscription to avoid alignment issues.

  3. Add ALTER SUBSCRIPTION ... SKIP.

  4. Optionally disable subscriptions on error.

  5. Update docs of logical replication for commit 8d74fc96db.

  6. Respect permissions within logical replication.

  7. Fix regression test failure caused by commit 8d74fc96db.

  8. Add a view to show the stats of subscription workers.

  9. Add logical change details to logical replication worker errcontext.

  10. Rename LOGICAL_REP_MSG_STREAM_END to LOGICAL_REP_MSG_STREAM_STOP.

  11. Fix typo in protocol.sgml.

  12. Remove unused argument in apply_handle_commit_internal().

  13. Fix replication of in-progress transactions in tablesync worker.

  14. Reorder pg_sequence columns to avoid alignment issue