Horton

Re: Minimal logical decoding on standbys

Alvaro Herrera <alvherre@2ndquadrant.com>

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From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: "Drouvot, Bertrand" <bdrouvot@amazon.com>
Cc: Ibrar Ahmed <ibrar.ahmad@gmail.com>, Amit Khandekar <amitdkhan.pg@gmail.com>, Andres Freund <andres@anarazel.de>, fabriziomello@gmail.com, tushar <tushar.ahuja@enterprisedb.com>, "[pgdg] Robert Haas" <robertmhaas@gmail.com>, Rahila Syed <rahila.syed@2ndquadrant.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2021-07-28T15:26:42Z
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. Reduce the log level in 035_standby_logical_decoding.pl.

  2. 035_standby_logical_decoding: Add missing waits for replication

  3. For cascading replication, wake physical and logical walsenders separately

  4. Handle logical slot conflicts on standby

  5. Support invalidating replication slots due to horizon and wal_level

  6. Prevent use of invalidated logical slot in CreateDecodingContext()

  7. Replace replication slot's invalidated_at LSN with an enum

  8. Pass down table relation into more index relation functions

  9. Assert only valid flag bits are passed to visibilitymap_set()

  10. Remove unused _bt_delitems_delete() argument.

  11. Add xl_btree_delete optimization.

On 2021-Jul-27, Drouvot, Bertrand wrote:

> diff --git a/src/backend/utils/cache/lsyscache.c b/src/backend/utils/cache/lsyscache.c

> +bool
> +get_rel_logical_catalog(Oid relid)
> +{
> +	bool	res;
> +	Relation rel;
> +
> +	/* assume previously locked */
> +	rel = table_open(relid, NoLock);
> +	res = RelationIsAccessibleInLogicalDecoding(rel);
> +	table_close(rel, NoLock);
> +
> +	return res;
> +}

So RelationIsAccessibleInLogicalDecoding() does a cheap check for
wal_level which can be done without opening the table; I think this
function should be rearranged to avoid doing that when not needed.
Also, putting this function in lsyscache.c seems somewhat wrong since
it's not merely accessing the system caches ...

I think it would be better to move this elsewhere (relcache.c, proto in
relcache.h, perhaps call it RelationIdIsAccessibleInLogicalDecoding) and
short-circuit for the check that can be done before opening the table.
At least the GiST code appears to be able to call this several times per
vacuum run, so it makes sense to short-circuit it for the fast case.

... though looking at the GiST code again I wonder if it would be more
sensible to just stash the table's Relation pointer somewhere in the
context structs instead of opening and closing it time and again.

-- 
Álvaro Herrera         PostgreSQL Developer  —  https://www.EnterpriseDB.com/
"Investigación es lo que hago cuando no sé lo que estoy haciendo"
(Wernher von Braun)