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From: Tom Lane <tgl@sss.pgh.pa.us>
To: Richard Guo <guofenglinux@gmail.com>
Cc: David Rowley <dgrowleyml@gmail.com>
Cc: Kirill Zdornyy <kirill@dineserve.com>
Cc: pgsql-bugs@lists.postgresql.org <pgsql-bugs@lists.postgresql.org>
Subject: Re: Error from array_agg when table has many rows
Date: Sat, 08 Mar 2025 10:50:01 -0500
Message-ID: <1297401.1741449001@sss.pgh.pa.us> (raw)
In-Reply-To: <CAMbWs49WUftz6gXGPSVrZJ0czZ1RCtQz4RxDZKEKZtYADvA6Sw@mail.gmail.com>
References: <atLI5Kce2ie1zcYjU0w_kjtVaxiYbYGTihrkLDmGZQnRDD4pnXukIATaABbnIj9pUnelC4ESvCXMm4HAyHg-v61XABaKpERj0A2IXzJZM7g=@dineserve.com>
	<CAMbWs49WUftz6gXGPSVrZJ0czZ1RCtQz4RxDZKEKZtYADvA6Sw@mail.gmail.com>

Richard Guo <guofenglinux@gmail.com> writes:
> We are performing deserialization during the final phase of the
> aggregation on data of type RECORD but we fail to provide a valid
> typmod (array_agg_deserialize() uses -1 as the typmod when calling the
> receiveproc).

> I haven't verified it, but I suspect it's related to 16fd03e95.

Yeah.  I don't think there is any way for array_agg_deserialize to
know the correct typmod, so what we have to do is disable using
partial aggregation in this case.  Fortunately there's a
policy-setting function that can be taught that, as attached.

			regards, tom lane

Attachments:

disable_partial_aggregation_on_RECORD.patch (text/x-diff, 1.1K) download
diff --git a/src/backend/parser/parse_agg.c b/src/backend/parser/parse_agg.c
index 9e567f3cc45..0ac8966e30f 100644
--- a/src/backend/parser/parse_agg.c
+++ b/src/backend/parser/parse_agg.c
@@ -2052,7 +2052,7 @@ resolve_aggregate_transtype(Oid aggfuncid,
 
 /*
  * agg_args_support_sendreceive
- *		Returns true if all non-byval of aggref's arg types have send and
+ *		Returns true if all non-byval types of aggref's args have send and
  *		receive functions.
  */
 bool
@@ -2067,6 +2067,15 @@ agg_args_support_sendreceive(Aggref *aggref)
 		TargetEntry *tle = (TargetEntry *) lfirst(lc);
 		Oid			type = exprType((Node *) tle->expr);
 
+		/*
+		 * RECORD is a special case: it has typsend/typreceive functions, but
+		 * record_recv only works if passed the correct typmod to identify the
+		 * specific anonymous record type.  array_agg_deserialize cannot do
+		 * that, so we have to disclaim support for the case.
+		 */
+		if (type == RECORDOID)
+			return false;
+
 		typeTuple = SearchSysCache1(TYPEOID, ObjectIdGetDatum(type));
 		if (!HeapTupleIsValid(typeTuple))
 			elog(ERROR, "cache lookup failed for type %u", type);

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