Horton

Re: Replication slot stats misgivings

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: vignesh C <vignesh21@gmail.com>, Andres Freund <andres@anarazel.de>, PostgreSQL-development <pgsql-hackers@postgresql.org>, Kyotaro HORIGUCHI <horiguchi.kyotaro@lab.ntt.co.jp>
Date: 2021-04-21T03:50:00Z
Lists: pgsql-hackers 
On Tue, Apr 20, 2021 at 7:54 PM Masahiko Sawada <sawada.mshk@gmail.com> wrote:
>

I have one question:

+ /*
+ * Create the replication slot stats hash table if we don't have
+ * it already.
+ */
+ if (replSlotStats == NULL)
  {
- if (namestrcmp(&replSlotStats[i].slotname, name) == 0)
- return i; /* found */
+ HASHCTL hash_ctl;
+
+ hash_ctl.keysize = sizeof(NameData);
+ hash_ctl.entrysize = sizeof(PgStat_StatReplSlotEntry);
+ hash_ctl.hcxt = pgStatLocalContext;
+
+ replSlotStats = hash_create("Replication slots hash",
+ PGSTAT_REPLSLOT_HASH_SIZE,
+ &hash_ctl,
+ HASH_ELEM | HASH_BLOBS | HASH_CONTEXT);
  }

It seems to me that the patch is always creating a hash table in
pgStatLocalContext?  AFAIU, we need to create it in pgStatLocalContext
when we read stats via backend_read_statsfile so that we can clear it
at the end of the transaction. The db/function stats seems to be doing
the same. Is there a reason why here we need to always create it in
pgStatLocalContext?

-- 
With Regards,
Amit Kapila.

Commits

  1. Doc: Update logical decoding stats information.

  2. Fix tests for replication slots stats.

  3. Update replication statistics after every stream/spill.

  4. Fix the computation of slot stats for 'total_bytes'.

  5. Another try to fix the test case added by commit f5fc2f5b23.

  6. Use HTAB for replication slot statistics.

  7. Fix test case added by commit f5fc2f5b23.

  8. Add information of total data processed to replication slot stats.

  9. Use NameData datatype for slotname in stats.