Justin Pryzby <pry...@telsasoft.com> writes:
> On Fri, Jul 26, 2024 at 10:53:30PM +0300, Alexander Korotkov wrote:
>> It would be nice to identify such cases and check which memory contexts are
>> growing and why.
> I reproduced the problem with this schema:
> SELECT format('CREATE TABLE p(i int, %s) PARTITION BY RANGE(i)',
> array_to_string(a, ', ')) FROM (SELECT array_agg(format('i%s int', i))a FROM
> generate_series(1,999)i);
> SELECT format('CREATE TABLE t%s PARTITION OF p FOR VALUES FROM (%s)TO(%s)',
> i,i,i+1) FROM generate_series(1,999)i;
> This used over 4 GB of RAM.
Interesting. This doesn't bloat particularly much in a regular
pg_restore, even with --transaction-size=1000; but it does in
pg_upgrade, as you say. I found that the bloat was occurring
during these long sequences of UPDATE commands issued by pg_upgrade:
-- For binary upgrade, recreate inherited column.
UPDATE pg_catalog.pg_attribute
SET attislocal = false
WHERE attname = 'i'
AND attrelid = '\"public\".\"t139\"'::pg_catalog.regclass;
-- For binary upgrade, recreate inherited column.
UPDATE pg_catalog.pg_attribute
SET attislocal = false
WHERE attname = 'i1'
AND attrelid = '\"public\".\"t139\"'::pg_catalog.regclass;
-- For binary upgrade, recreate inherited column.
UPDATE pg_catalog.pg_attribute
SET attislocal = false
WHERE attname = 'i2'
AND attrelid = '\"public\".\"t139\"'::pg_catalog.regclass;
I think the problem is basically that each one of these commands
causes a relcache inval, for which we can't reclaim space right
away, so that we end up consuming O(N^2) cache space for an
N-column inherited table.
It's fairly easy to fix things so that this example doesn't cause
that to happen: we just need to issue these updates as one command
not N commands per table. See attached. However, I fear this should
just be considered a draft, because the other code for binary upgrade
in the immediate vicinity is just as aggressively stupid and
unoptimized as this bit, and can probably also be driven to O(N^2)
behavior with enough CHECK constraints etc. We've gone out of our way
to make ALTER TABLE capable of handling many updates to a table's DDL
in one command, but whoever wrote this code appears not to have read
that memo, or at least to have believed that performance of pg_upgrade
isn't of concern.
> Note that there seemed to be no issue when I created 999 tables without
> partitioning:
> SELECT format('CREATE TABLE t%s(LIKE p)', i,i,i+1) FROM
> generate_series(1,999)i;
Yeah, because then we don't need to play games with attislocal.
regards, tom lane
diff --git a/src/bin/pg_dump/pg_dump.c b/src/bin/pg_dump/pg_dump.c
index b8b1888bd3..19f98bdf43 100644
--- a/src/bin/pg_dump/pg_dump.c
+++ b/src/bin/pg_dump/pg_dump.c
@@ -16094,6 +16094,12 @@ dumpTableSchema(Archive *fout, const TableInfo *tbinfo)
tbinfo->relkind == RELKIND_FOREIGN_TABLE ||
tbinfo->relkind == RELKIND_PARTITIONED_TABLE))
{
+ bool firstinhcol = true;
+
+ /*
+ * Drop any dropped columns. We don't really expect there to be a
+ * lot, else this code would be pretty inefficient.
+ */
for (j = 0; j < tbinfo->numatts; j++)
{
if (tbinfo->attisdropped[j])
@@ -16120,18 +16126,37 @@ dumpTableSchema(Archive *fout, const TableInfo *tbinfo)
appendPQExpBuffer(q, "DROP COLUMN %s;\n",
fmtId(tbinfo->attnames[j]));
}
- else if (!tbinfo->attislocal[j])
+ }
+
+ /*
+ * Fix up inherited columns. There could be a lot of these, so we
+ * do the operation in a single SQL command; otherwise, we risk
+ * O(N^2) relcache bloat thanks to repeatedly invalidating the
+ * table's relcache entry.
+ */
+ for (j = 0; j < tbinfo->numatts; j++)
+ {
+ if (!tbinfo->attisdropped[j] &&
+ !tbinfo->attislocal[j])
{
- appendPQExpBufferStr(q, "\n-- For binary upgrade, recreate inherited column.\n");
- appendPQExpBufferStr(q, "UPDATE pg_catalog.pg_attribute\n"
- "SET attislocal = false\n"
- "WHERE attname = ");
+ if (firstinhcol)
+ {
+ appendPQExpBufferStr(q, "\n-- For binary upgrade, recreate inherited columns.\n");
+ appendPQExpBufferStr(q, "UPDATE pg_catalog.pg_attribute\n"
+ "SET attislocal = false\n"
+ "WHERE attrelid = ");
+ appendStringLiteralAH(q, qualrelname, fout);
+ appendPQExpBufferStr(q, "::pg_catalog.regclass\n"
+ " AND attname IN (");
+ firstinhcol = false;
+ }
+ else
+ appendPQExpBufferStr(q, ", ");
appendStringLiteralAH(q, tbinfo->attnames[j], fout);
- appendPQExpBufferStr(q, "\n AND attrelid = ");
- appendStringLiteralAH(q, qualrelname, fout);
- appendPQExpBufferStr(q, "::pg_catalog.regclass;\n");
}
}
+ if (!firstinhcol)
+ appendPQExpBufferStr(q, ");\n");
/*
* Add inherited CHECK constraints, if any.
