Prevent parallel DecompressChunk in queries with LIMIT

In queries with LIMIT a parallel plan is quite often less desirable due to startup cost and changed ordering behaviour.
timescale · May 3, 2024 · f6c73ea · f6c73ea
1 parent 396dd0c
commit f6c73ea
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Showing 2 changed files with 109 additions and 145 deletions.
diff --git a/tsl/src/nodes/decompress_chunk/decompress_chunk.c b/tsl/src/nodes/decompress_chunk/decompress_chunk.c
@@ -1006,7 +1006,7 @@ ts_decompress_chunk_generate_paths(PlannerInfo *root, RelOptInfo *chunk_rel, Hyp
 	 * if it's planned */
 	compressed_rel->pathlist = NIL;
 	/* create parallel paths */
-	if (compressed_rel->consider_parallel)
+	if (compressed_rel->consider_parallel && root->limit_tuples <= 0)
 	{
 		foreach (lc, compressed_rel->partial_pathlist)
 		{

diff --git a/tsl/test/shared/expected/transparent_decompress_chunk-15.out b/tsl/test/shared/expected/transparent_decompress_chunk-15.out
@@ -142,14 +142,12 @@ QUERY PLAN
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE device_id IS NOT NULL ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-                           Filter: (device_id IS NOT NULL)
-(8 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               ->  Seq Scan on compress_hyper_X_X_chunk
+                     Filter: (device_id IS NOT NULL)
+(6 rows)
 
 :PREFIX SELECT * FROM :TEST_TABLE WHERE device_id IS NULL ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
@@ -187,26 +185,22 @@ QUERY PLAN
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE device_id = v0 ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Filter: (device_id = v0)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-(8 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Filter: (device_id = v0)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+(6 rows)
 
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE device_id < v1 ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Filter: (device_id < v1)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-(8 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Filter: (device_id < v1)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+(6 rows)
 
 -- test expressions
 :PREFIX SELECT * FROM :TEST_TABLE WHERE device_id = 1 + 4 / 2 ORDER BY time, device_id LIMIT 10;
@@ -222,14 +216,12 @@ QUERY PLAN
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE device_id = length(substring(version(), 1, 3)) ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time"
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Filter: (device_id = length("substring"(version(), 1, 3)))
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-(8 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time"
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Filter: (device_id = length("substring"(version(), 1, 3)))
+               ->  Seq Scan on compress_hyper_X_X_chunk
+(6 rows)
 
 -- test segment meta pushdown
 -- order by column and const
@@ -245,133 +237,111 @@ QUERY PLAN
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE time < '2000-01-01 1:00:00+0' ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Vectorized Filter: ("time" < 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-                           Filter: (_ts_meta_min_1 < 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
-(9 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Vectorized Filter: ("time" < 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+                     Filter: (_ts_meta_min_1 < 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
+(7 rows)
 
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE time <= '2000-01-01 1:00:00+0' ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Vectorized Filter: ("time" <= 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-                           Filter: (_ts_meta_min_1 <= 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
-(9 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Vectorized Filter: ("time" <= 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+                     Filter: (_ts_meta_min_1 <= 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
+(7 rows)
 
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE time >= '2000-01-01 1:00:00+0' ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Vectorized Filter: ("time" >= 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-                           Filter: (_ts_meta_max_1 >= 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
-(9 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Vectorized Filter: ("time" >= 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+                     Filter: (_ts_meta_max_1 >= 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
+(7 rows)
 
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE time > '2000-01-01 1:00:00+0' ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Vectorized Filter: ("time" > 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-                           Filter: (_ts_meta_max_1 > 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
-(9 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Vectorized Filter: ("time" > 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+                     Filter: (_ts_meta_max_1 > 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
+(7 rows)
 
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE '2000-01-01 1:00:00+0' < time ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Vectorized Filter: ("time" > 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-                           Filter: (_ts_meta_max_1 > 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
-(9 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Vectorized Filter: ("time" > 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+                     Filter: (_ts_meta_max_1 > 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone)
+(7 rows)
 
 --pushdowns between order by and segment by columns
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE v0 < 1 ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Vectorized Filter: (v0 < 1)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-(8 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Vectorized Filter: (v0 < 1)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+(6 rows)
 
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE v0 < device_id ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Filter: (v0 < device_id)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-(8 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Filter: (v0 < device_id)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+(6 rows)
 
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE device_id < v0 ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Filter: (device_id < v0)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-(8 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Filter: (device_id < v0)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+(6 rows)
 
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE v1 = device_id ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Filter: (v1 = device_id)
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-(8 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Filter: (v1 = device_id)
+               ->  Seq Scan on compress_hyper_X_X_chunk
+(6 rows)
 
 --pushdown between two order by column (not pushed down)
 :PREFIX SELECT * FROM :TEST_TABLE WHERE v0 = v1 ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit (actual rows=0 loops=1)
-   ->  Gather Merge (actual rows=0 loops=1)
-         Workers Planned: 2
-         Workers Launched: 2
-         ->  Sort (actual rows=0 loops=2)
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               Worker 0:  Sort Method: quicksort 
-               Worker 1:  Sort Method: quicksort 
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk (actual rows=0 loops=2)
-                     Filter: (v0 = v1)
-                     Rows Removed by Filter: 8995
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk (actual rows=10 loops=2)
-(12 rows)
+   ->  Sort (actual rows=0 loops=1)
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         Sort Method: quicksort 
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk (actual rows=0 loops=1)
+               Filter: (v0 = v1)
+               Rows Removed by Filter: 17990
+               ->  Seq Scan on compress_hyper_X_X_chunk (actual rows=20 loops=1)
+(8 rows)
 
 --pushdown of quals on order by and segment by cols anded together
 :PREFIX_VERBOSE SELECT * FROM :TEST_TABLE WHERE time > '2000-01-01 1:00:00+0' AND device_id = 1 ORDER BY time, device_id LIMIT 10;
@@ -393,27 +363,23 @@ QUERY PLAN
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE time > '2000-01-01 1:00:00+0' OR device_id = 1 ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Filter: (("time" > 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone) OR (device_id = 1))
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-(8 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Filter: (("time" > 'Fri Dec 31 17:00:00 1999 PST'::timestamp with time zone) OR (device_id = 1))
+               ->  Seq Scan on compress_hyper_X_X_chunk
+(6 rows)
 
 --functions not yet optimized
 :PREFIX_NO_VERBOSE SELECT * FROM :TEST_TABLE WHERE time < now() ORDER BY time, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     Vectorized Filter: ("time" < now())
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-(8 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time", _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               Vectorized Filter: ("time" < now())
+               ->  Seq Scan on compress_hyper_X_X_chunk
+(6 rows)
 
 -- test sort optimization interaction
 :PREFIX_NO_VERBOSE SELECT time FROM :TEST_TABLE ORDER BY time DESC LIMIT 10;
@@ -428,13 +394,11 @@ QUERY PLAN
 :PREFIX_NO_VERBOSE SELECT time, device_id FROM :TEST_TABLE ORDER BY time DESC, device_id LIMIT 10;
 QUERY PLAN
  Limit
-   ->  Gather Merge
-         Workers Planned: 2
-         ->  Sort
-               Sort Key: _hyper_X_X_chunk."time" DESC, _hyper_X_X_chunk.device_id
-               ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
-                     ->  Parallel Seq Scan on compress_hyper_X_X_chunk
-(7 rows)
+   ->  Sort
+         Sort Key: _hyper_X_X_chunk."time" DESC, _hyper_X_X_chunk.device_id
+         ->  Custom Scan (DecompressChunk) on _hyper_X_X_chunk
+               ->  Seq Scan on compress_hyper_X_X_chunk
+(5 rows)
 
 :PREFIX_NO_VERBOSE SELECT time, device_id FROM :TEST_TABLE ORDER BY device_id, time DESC LIMIT 10;
 QUERY PLAN