From 185e304263347d0979832f7a08a812872d136b18 Mon Sep 17 00:00:00 2001 From: Richard Guo Date: Wed, 8 Oct 2025 17:01:48 +0900 Subject: Allow negative aggtransspace to indicate unbounded state size This patch reuses the existing aggtransspace in pg_aggregate to signal that an aggregate's transition state can grow unboundedly. If aggtransspace is set to a negative value, it now indicates that the transition state may consume unpredictable or large amounts of memory, such as in aggregates like array_agg or string_agg that accumulate input rows. This information can be used by the planner to avoid applying memory-sensitive optimizations (e.g., eager aggregation) when there is a risk of excessive memory usage during partial aggregation. Bump catalog version. Per idea from Robert Haas, though applied differently than originally suggested. Discussion: https://postgr.es/m/CA+TgmoYbkvYwLa+1vOP7RDY7kO2=A7rppoPusoRXe44VDOGBPg@mail.gmail.com --- doc/src/sgml/catalogs.sgml | 5 ++++- doc/src/sgml/ref/create_aggregate.sgml | 11 ++++++++--- 2 files changed, 12 insertions(+), 4 deletions(-) (limited to 'doc/src') diff --git a/doc/src/sgml/catalogs.sgml b/doc/src/sgml/catalogs.sgml index e9095bedf21..3acc2222a87 100644 --- a/doc/src/sgml/catalogs.sgml +++ b/doc/src/sgml/catalogs.sgml @@ -596,7 +596,10 @@ Approximate average size (in bytes) of the transition state - data, or zero to use a default estimate + data. A positive value provides an estimate; zero means to + use a default estimate. A negative value indicates the state + data can grow unboundedly in size, such as when the aggregate + accumulates input rows (e.g., array_agg, string_agg). diff --git a/doc/src/sgml/ref/create_aggregate.sgml b/doc/src/sgml/ref/create_aggregate.sgml index 222e0aa5c9d..0472ac2e874 100644 --- a/doc/src/sgml/ref/create_aggregate.sgml +++ b/doc/src/sgml/ref/create_aggregate.sgml @@ -384,9 +384,13 @@ SELECT col FROM tab ORDER BY col USING sortop LIMIT 1; The approximate average size (in bytes) of the aggregate's state value. If this parameter is omitted or is zero, a default estimate is used - based on the state_data_type. + based on the state_data_type. If set to a + negative value, it indicates the state data can grow unboundedly in + size, such as when the aggregate accumulates input rows (e.g., + array_agg, string_agg). The planner uses this value to estimate the memory required for a - grouped aggregate query. + grouped aggregate query and to avoid optimizations that may cause + excessive memory usage. @@ -568,7 +572,8 @@ SELECT col FROM tab ORDER BY col USING sortop LIMIT 1; The approximate average size (in bytes) of the aggregate's state value, when using moving-aggregate mode. This works the same as - state_data_size. + state_data_size, except that negative + values are not used to indicate unbounded state size. -- cgit v1.2.3