Fix DecompressChunk path generation

The non-parallel pathes generated by DecompressChunk were
incorrectly marked as parallel_safe even when the child scan
was not parallel aware. Leading to incorrect query results
when those pathes were used in a parallel plan.
Additionaly DecompressChunk code didnt set total_table_pages on
PlannerInfo leading to an assertion failure in BitmapHeapscan
path creation.

tsl/src/nodes/decompress_chunk/decompress_chunk.c

@@ -6,6 +6,7 @@
 
 #include <postgres.h>
 #include <catalog/pg_operator.h>
+#include <miscadmin.h>
 #include <nodes/bitmapset.h>
 #include <nodes/makefuncs.h>
 #include <nodes/nodeFuncs.h>
@@ -16,7 +17,6 @@
 #include <utils/builtins.h>
 #include <utils/lsyscache.h>
 #include <utils/typcache.h>
-#include <miscadmin.h>
 
 #include "compat.h"
 #if PG12_LT
@@ -946,11 +946,13 @@ decompress_chunk_path_create(PlannerInfo *root, CompressionInfo *info, int paral
 	path->cpath.flags = 0;
 	path->cpath.methods = &decompress_chunk_path_methods;
 
-	Assert(parallel_workers == 0 || compressed_path->parallel_safe);
-
-	path->cpath.path.parallel_aware = false;
-	path->cpath.path.parallel_safe = compressed_path->parallel_safe;
+	/* To prevent a non-parallel path with this node appearing
+	 * in a parallel plan we only set parallel_safe to true
+	 * when parallel_workers is greater than 0 which is only
+	 * the case when creating partial paths. */
+	path->cpath.path.parallel_safe = parallel_workers > 0;
 	path->cpath.path.parallel_workers = parallel_workers;
+	path->cpath.path.parallel_aware = false;
 
 	path->cpath.custom_paths = list_make1(compressed_path);
 	path->reverse = false;
@@ -970,6 +972,10 @@ create_compressed_scan_paths(PlannerInfo *root, RelOptInfo *compressed_rel, int
 {
 	Path *compressed_path;
 
+	/* clamp total_table_pages to 10 pages since this is the
+	 * minimum estimate for number of pages */
+	root->total_table_pages = Max(compressed_rel->pages, 10);
+
 	/* create non parallel scan path */
 	compressed_path = create_seqscan_path(root, compressed_rel, NULL, 0);
 	add_path(compressed_rel, compressed_path);

tsl/test/shared/expected/decompress_placeholdervar.out

@@ -76,3 +76,64 @@ ORDER BY 1,2;
 
 DROP TABLE decompress_phv_ping;
 DROP TABLE decompress_phv_device;
+-- test assertion failure in bitmapheapscan path creation
+-- GH Issue #2211
+CREATE TABLE tickers (
+  time TIMESTAMPTZ,
+  microseconds INT,
+  fk_exchange SMALLINT,
+  fk_trade_pair SMALLINT
+);
+CREATE INDEX ON tickers (fk_exchange, fk_trade_pair, time DESC, microseconds DESC);
+SELECT
+  table_name
+FROM
+  create_hypertable('tickers', 'time');
+NOTICE:  adding not-null constraint to column "time"
+ table_name 
+------------
+ tickers
+(1 row)
+
+ALTER TABLE tickers SET (timescaledb.compress, timescaledb.compress_segmentby = 'fk_exchange,
+  fk_trade_pair', timescaledb.compress_orderby = 'time DESC, microseconds DESC');
+INSERT INTO tickers
+SELECT
+  '2000-01-01',
+  0,
+  i,
+  j
+FROM
+  generate_series(1, 20) i,
+  generate_series(1, 40) j;
+SELECT
+  substr(compress_chunk(tableoid::REGCLASS)::TEXT, 1, 29)
+FROM
+  tickers
+GROUP BY
+  tableoid;
+            substr             
+-------------------------------
+ _timescaledb_internal._hyper_
+(1 row)
+
+-- make sure we get bitmapheapscan
+SET enable_indexscan TO FALSE;
+SELECT
+  *
+FROM
+  tickers
+WHERE
+  time >= '2000-01-01'
+  AND time < '2020-08-02T00:00Z'
+  AND fk_exchange = 4
+  AND fk_trade_pair = 29
+ORDER BY
+  time DESC,
+  microseconds DESC;
+             time             | microseconds | fk_exchange | fk_trade_pair 
+------------------------------+--------------+-------------+---------------
+ Sat Jan 01 00:00:00 2000 PST |            0 |           4 |            29
+(1 row)
+
+DROP TABLE tickers;

tsl/test/shared/sql/decompress_placeholdervar.sql

@@ -52,3 +52,56 @@ ORDER BY 1,2;
 DROP TABLE decompress_phv_ping;
 DROP TABLE decompress_phv_device;
 
+-- test assertion failure in bitmapheapscan path creation
+-- GH Issue #2211
+CREATE TABLE tickers (
+  time TIMESTAMPTZ,
+  microseconds INT,
+  fk_exchange SMALLINT,
+  fk_trade_pair SMALLINT
+);
+
+CREATE INDEX ON tickers (fk_exchange, fk_trade_pair, time DESC, microseconds DESC);
+
+SELECT
+  table_name
+FROM
+  create_hypertable('tickers', 'time');
+
+ALTER TABLE tickers SET (timescaledb.compress, timescaledb.compress_segmentby = 'fk_exchange,
+  fk_trade_pair', timescaledb.compress_orderby = 'time DESC, microseconds DESC');
+
+INSERT INTO tickers
+SELECT
+  '2000-01-01',
+  0,
+  i,
+  j
+FROM
+  generate_series(1, 20) i,
+  generate_series(1, 40) j;
+
+SELECT
+  substr(compress_chunk(tableoid::REGCLASS)::TEXT, 1, 29)
+FROM
+  tickers
+GROUP BY
+  tableoid;
+
+-- make sure we get bitmapheapscan
+SET enable_indexscan TO FALSE;
+
+SELECT
+  *
+FROM
+  tickers
+WHERE
+  time >= '2000-01-01'
+  AND time < '2020-08-02T00:00Z'
+  AND fk_exchange = 4
+  AND fk_trade_pair = 29
+ORDER BY
+  time DESC,
+  microseconds DESC;
+
+DROP TABLE tickers;