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Improve DecompressChunk qual pushdown

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Allow pushdown of RelabelType expressions into the scan below the
DecompressChunk node. When using varchar columns as segmentby
columns constraints on those columns would not be pushed down
because postgres would inject RelabelType nodes that where not
accepted as valid expression for pushdown leading to bad performance
because the filter could only be applied after decompression.

Fixes #3351
This commit is contained in:
Sven Klemm 2021-06-25 16:42:59 +02:00 committed by Sven Klemm
parent e57155fdc0
commit 45a7abc4de
4 changed files with 107 additions and 0 deletions
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1
CHANGELOG.md
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@ -11,6 +11,7 @@ accidentally triggering the load of a previous DB version.**
* #3327 Make aggregates in caggs fully qualified
* #3336 Fix pg_init_privs objsubid handling
* #3345 Fix SkipScan distinct column identification
* #3367 Improve DecompressChunk qual pushdown
**Thanks**
* @db-adrian for reporting an issue when accessing cagg view through postgres_fdw

1
tsl/src/nodes/decompress_chunk/qual_pushdown.c
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@ -357,6 +357,7 @@ modify_expression(Node *node, QualPushdownContext *context)
/* opexpr will still be checked for segment by columns */
break;
}
case T_RelabelType:
case T_ScalarArrayOpExpr:
case T_List:
case T_Const:

84
tsl/test/expected/compression_qualpushdown.out
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@ -176,3 +176,87 @@ from metaseg_tab
where fmid = 56
and end_dt::date = 'dec 2010'::date;
ERROR: invalid input syntax for type date: "dec 2010" at character 86
-- test casts between different char types are pushed down
CREATE TABLE pushdown_relabel(time timestamptz NOT NULL, dev_vc varchar(10), dev_c char(10));
SELECT table_name FROM create_hypertable('pushdown_relabel', 'time');
table_name
------------------
pushdown_relabel
(1 row)
ALTER TABLE pushdown_relabel SET (timescaledb.compress, timescaledb.compress_segmentby='dev_vc,dev_c');
INSERT INTO pushdown_relabel SELECT '2000-01-01','varchar','char';
SELECT compress_chunk(i) from show_chunks('pushdown_relabel') i;
compress_chunk
----------------------------------------
_timescaledb_internal._hyper_5_6_chunk
(1 row)
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar';
QUERY PLAN
----------------------------------------------------
Custom Scan (DecompressChunk) on _hyper_5_6_chunk
-> Seq Scan on compress_hyper_6_7_chunk
Filter: ((dev_vc)::text = 'varchar'::text)
(3 rows)
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_c = 'char';
QUERY PLAN
---------------------------------------------------
Custom Scan (DecompressChunk) on _hyper_5_6_chunk
-> Seq Scan on compress_hyper_6_7_chunk
Filter: (dev_c = 'char'::bpchar)
(3 rows)
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar' AND dev_c = 'char';
QUERY PLAN
-----------------------------------------------------------------------------------
Custom Scan (DecompressChunk) on _hyper_5_6_chunk
-> Seq Scan on compress_hyper_6_7_chunk
Filter: (((dev_vc)::text = 'varchar'::text) AND (dev_c = 'char'::bpchar))
(3 rows)
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar'::char(10) AND dev_c = 'char'::varchar;
QUERY PLAN
-------------------------------------------------------------------------------------------------
Custom Scan (DecompressChunk) on _hyper_5_6_chunk
-> Seq Scan on compress_hyper_6_7_chunk
Filter: (((dev_vc)::bpchar = 'varchar '::character(10)) AND (dev_c = 'char'::bpchar))
(3 rows)
-- test again with index scans
SET enable_seqscan TO false;
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar';
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------
Custom Scan (DecompressChunk) on _hyper_5_6_chunk
-> Index Scan using compress_hyper_6_7_chunk__compressed_hypertable_6_dev_vc__ts_me on compress_hyper_6_7_chunk
Index Cond: ((dev_vc)::text = 'varchar'::text)
(3 rows)
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_c = 'char';
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------
Custom Scan (DecompressChunk) on _hyper_5_6_chunk
-> Index Scan using compress_hyper_6_7_chunk__compressed_hypertable_6_dev_c__ts_met on compress_hyper_6_7_chunk
Index Cond: (dev_c = 'char'::bpchar)
(3 rows)
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar' AND dev_c = 'char';
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------
Custom Scan (DecompressChunk) on _hyper_5_6_chunk
-> Index Scan using compress_hyper_6_7_chunk__compressed_hypertable_6_dev_c__ts_met on compress_hyper_6_7_chunk
Index Cond: (dev_c = 'char'::bpchar)
Filter: ((dev_vc)::text = 'varchar'::text)
(4 rows)
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar'::char(10) AND dev_c = 'char'::varchar;
QUERY PLAN
--------------------------------------------------------------------------------------------------------------------
Custom Scan (DecompressChunk) on _hyper_5_6_chunk
-> Index Scan using compress_hyper_6_7_chunk__compressed_hypertable_6_dev_c__ts_met on compress_hyper_6_7_chunk
Index Cond: (dev_c = 'char'::bpchar)
Filter: ((dev_vc)::bpchar = 'varchar '::character(10))
(4 rows)

21
tsl/test/sql/compression_qualpushdown.sql
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@ -98,3 +98,24 @@ select factorid, end_dt, logret
from metaseg_tab
where fmid = 56
and end_dt::date = 'dec 2010'::date;
-- test casts between different char types are pushed down
CREATE TABLE pushdown_relabel(time timestamptz NOT NULL, dev_vc varchar(10), dev_c char(10));
SELECT table_name FROM create_hypertable('pushdown_relabel', 'time');
ALTER TABLE pushdown_relabel SET (timescaledb.compress, timescaledb.compress_segmentby='dev_vc,dev_c');
INSERT INTO pushdown_relabel SELECT '2000-01-01','varchar','char';
SELECT compress_chunk(i) from show_chunks('pushdown_relabel') i;
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar';
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_c = 'char';
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar' AND dev_c = 'char';
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar'::char(10) AND dev_c = 'char'::varchar;
-- test again with index scans
SET enable_seqscan TO false;
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar';
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_c = 'char';
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar' AND dev_c = 'char';
EXPLAIN (costs off) SELECT * FROM pushdown_relabel WHERE dev_vc = 'varchar'::char(10) AND dev_c = 'char'::varchar;