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Disable direct compress when RETURNING clause references system columns
Direct compress stores the tuple in compressed form instead of a regular heap tuple, so system columns like ctid or xmin never get a meaningful value. Fall back to the normal insert path when RETURNING references them. tableoid is fine because the returning projection sets it explicitly.
1 parent 93f9f87 commit e7aaf4c

3 files changed

Lines changed: 162 additions & 1 deletion

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‎src/nodes/modify_hypertable.c‎

Lines changed: 30 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -5,9 +5,11 @@
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*/
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#include <postgres.h>
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#include <access/sysattr.h>
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#include <nodes/execnodes.h>
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#include <nodes/makefuncs.h>
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#include <nodes/nodeFuncs.h>
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#include <optimizer/optimizer.h>
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#include <parser/parsetree.h>
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#include <utils/snapmgr.h>
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@@ -69,6 +71,34 @@ should_use_direct_compress(ModifyHypertableState *state)
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return false;
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}
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/*
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* Direct compress stores the tuple in compressed form instead of a
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* regular heap tuple, so system columns like ctid or xmin never get a
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* meaningful value. Fall back to the normal insert path when RETURNING
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* references them. tableoid is fine because the returning projection
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* sets it explicitly.
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*/
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ModifyTable *mt = castNode(ModifyTable, mtstate->ps.plan);
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if (mt->returningLists)
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{
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Bitmapset *attnos = NULL;
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pull_varattnos((Node *) linitial(mt->returningLists),
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resultRelInfo->ri_RangeTableIndex,
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&attnos);
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int attno = -1;
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while ((attno = bms_next_member(attnos, attno)) >= 0)
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{
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AttrNumber sysattno = attno + FirstLowInvalidHeapAttributeNumber;
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if (sysattno < 0 && sysattno != TableOidAttributeNumber)
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{
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ereport(WARNING,
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(errmsg("disabling direct compress because the RETURNING clause "
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"references system columns")));
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return false;
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}
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}
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}
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Plan *subplan = mtstate->ps.plan->lefttree;
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if (subplan->plan_rows < 10)
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{

‎tsl/test/expected/direct_compress_insert.out‎

Lines changed: 101 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -997,11 +997,111 @@ SELECT count(*), min(label), max(label) FROM inserted;
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-------+-------+------
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20 | d0:10 | d1:9
999999

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-- RETURNING a system column falls back to the normal insert path, except
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-- tableoid which the returning projection sets explicitly.
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EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
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INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
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FROM generate_series(1, 20) i RETURNING ctid;
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WARNING: disabling direct compress because the RETURNING clause references system columns
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--- QUERY PLAN ---
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Custom Scan (ModifyHypertable)
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Direct Compress: false
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-> Insert on dc_ret
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-> Function Scan on generate_series i
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EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
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INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
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FROM generate_series(1, 20) i RETURNING xmin;
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WARNING: disabling direct compress because the RETURNING clause references system columns
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--- QUERY PLAN ---
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Custom Scan (ModifyHypertable)
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Direct Compress: false
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-> Insert on dc_ret
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-> Function Scan on generate_series i
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EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
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INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
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FROM generate_series(1, 20) i RETURNING cmin;
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WARNING: disabling direct compress because the RETURNING clause references system columns
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--- QUERY PLAN ---
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Custom Scan (ModifyHypertable)
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Direct Compress: false
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-> Insert on dc_ret
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-> Function Scan on generate_series i
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EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
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INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
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FROM generate_series(1, 20) i RETURNING xmax;
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WARNING: disabling direct compress because the RETURNING clause references system columns
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--- QUERY PLAN ---
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Custom Scan (ModifyHypertable)
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Direct Compress: false
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-> Insert on dc_ret
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-> Function Scan on generate_series i
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EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
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INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
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FROM generate_series(1, 20) i RETURNING cmax;
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WARNING: disabling direct compress because the RETURNING clause references system columns
1046+
--- QUERY PLAN ---
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Custom Scan (ModifyHypertable)
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Direct Compress: false
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-> Insert on dc_ret
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-> Function Scan on generate_series i
1051+
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-- tableoid stays on the direct compress path
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EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
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INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
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FROM generate_series(1, 20) i RETURNING tableoid;
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--- QUERY PLAN ---
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Custom Scan (ModifyHypertable)
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Direct Compress: true
1059+
-> Insert on dc_ret
1060+
-> Function Scan on generate_series i
1061+
1062+
-- ctid falls back and returns real tuple ids
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WITH inserted AS (
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INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 day'), 'd' || (i % 2)::text, i
1065+
FROM generate_series(1, 20) i RETURNING ctid AS c, val
1066+
)
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SELECT count(*), bool_and(c IS NOT NULL), min(val), max(val) FROM inserted;
1068+
WARNING: disabling direct compress because the RETURNING clause references system columns
1069+
count | bool_and | min | max
1070+
-------+----------+-----+-----
1071+
20 | t | 1 | 20
1072+
1073+
-- tableoid on the direct compress path holds the target chunk (all 20 rows
1074+
-- land in one chunk, so every RETURNING row reports the same chunk)
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INSERT INTO dc_ret SELECT '2025-06-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
1076+
FROM generate_series(1, 20) i RETURNING tableoid::regclass AS chunk;
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chunk
1078+
------------------------------------------
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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_timescaledb_internal._hyper_16_67_chunk
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10001100
-- rows were actually inserted
10011101
SELECT count(*) FROM dc_ret;
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count
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-------
1004-
40
1104+
80
10051105

10061106
RESET timescaledb.enable_direct_compress_insert;
10071107
DROP TABLE dc_ret;

‎tsl/test/sql/direct_compress_insert.sql‎

Lines changed: 31 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -590,6 +590,37 @@ WITH inserted AS (
590590
FROM generate_series(1, 20) i RETURNING device || ':' || val AS label
591591
)
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SELECT count(*), min(label), max(label) FROM inserted;
593+
-- RETURNING a system column falls back to the normal insert path, except
594+
-- tableoid which the returning projection sets explicitly.
595+
EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
596+
INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
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FROM generate_series(1, 20) i RETURNING ctid;
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EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
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INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
600+
FROM generate_series(1, 20) i RETURNING xmin;
601+
EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
602+
INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
603+
FROM generate_series(1, 20) i RETURNING cmin;
604+
EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
605+
INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
606+
FROM generate_series(1, 20) i RETURNING xmax;
607+
EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
608+
INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
609+
FROM generate_series(1, 20) i RETURNING cmax;
610+
-- tableoid stays on the direct compress path
611+
EXPLAIN (COSTS OFF, SUMMARY OFF, TIMING OFF)
612+
INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
613+
FROM generate_series(1, 20) i RETURNING tableoid;
614+
-- ctid falls back and returns real tuple ids
615+
WITH inserted AS (
616+
INSERT INTO dc_ret SELECT '2025-01-01'::timestamptz + (i * INTERVAL '1 day'), 'd' || (i % 2)::text, i
617+
FROM generate_series(1, 20) i RETURNING ctid AS c, val
618+
)
619+
SELECT count(*), bool_and(c IS NOT NULL), min(val), max(val) FROM inserted;
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-- tableoid on the direct compress path holds the target chunk (all 20 rows
621+
-- land in one chunk, so every RETURNING row reports the same chunk)
622+
INSERT INTO dc_ret SELECT '2025-06-01'::timestamptz + (i * INTERVAL '1 minute'), 'd' || (i % 2)::text, i
623+
FROM generate_series(1, 20) i RETURNING tableoid::regclass AS chunk;
593624
-- rows were actually inserted
594625
SELECT count(*) FROM dc_ret;
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RESET timescaledb.enable_direct_compress_insert;

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