After thinking about the described issues for a while, my proposal is to
completely revamp the way this feature works. See below.
Now, the proposal seems awfully invasive, but it's *the* way I see to
avoid the pgstat traffic. For pg14, maybe we can live with it, and just
use the smaller patches that Horiguchi-san and I have posted, which
solve the other issues; also, Euler Taveira suggested that we could add
a reloption to turn the feature off completely for some tables (maybe
make it off by default and have a reloption to turn it on for specific
partition hierarchies), so that it doesn't cause unduly pain for people
with large partitioning hierarchies.
* PgStat_StatTabEntry gets a new "Oid reportAncestorOid" member. This is
the OID of a single partitioned ancestor, to which the changed-tuple
counts are propagated up.
Normally this is the topmost ancestor; but if the user wishes some
intermediate ancestor to receive the counts they can use
ALTER TABLE the_intermediate_ancestor SET (autovacuum_enabled=on).
* Corollary 1: for the normal case of single-level partitioning, the
parent partitioned table behaves as currently.
* Corollary 2: for multi-level partitioning with no especially
configured intermediate ancestors, only the leaf partitions and the
top-level partitioned table will be analyzed. Intermediate ancestors
are ignored by autovacuum.
* Corollary 3: for multi-level partitioning with some intermediate
ancestor(s) marked as autovacuum_enabled=on, that ancestor will
receive all the counts from all of its partitions, so it will get
analyzed itself; and it'll also forward those counts up to its
report-ancestor.
* On ALTER TABLE .. ATTACH PARTITION or CREATE TABLE PARTITION AS,
we send a message to collector with the analyze-ancestor OID.
* Backends running manual ANALYZE as well as autovacuum will examine
each table's "relispartition" flag and its pgstat table entry; if it
is a partition and doesn't have reportAncestorOid set, determine which
ancestor should analyze counts be reported to; include this OID in the
regular PgStat_MsgAnalyze. This fixes the situation after a crash or
other stats reset. Also, it's not unduly expensive to do, because
it's only in the rare case that the value sent by ATTACH was lost.
* Possible race condition in the previous step may cause multiple
backends to send the same info. Not a serious problem so we don't try
to handle it.
* When tuple change counts for a partition are received by
pgstat_recv_tabstat, they are propagated up to the indicated parent
table in addition to being saved in the table itself.
(Bonus points: when a table is attached or detached as a partition,
the live tuples count is propagated to the newly acquired parent.)
What do people think of this?
--
Álvaro Herrera 39°49'30"S 73°17'W — https://www.EnterpriseDB.com/
