Don't leak Chunks in classify_relation

[akuzm]

This function is called often, at least 4 times per chunk, so these add
up. Freeing these chunks allows us to save memory. Ideally, we should
fix the function not to look up the chunk anew each time.

Also make a couple other tweaks that reduce memory usage for planning.

Fixes #2486

For a simple query explain delete from t where value = 1.1, where t is a distributed hypertable with 106 partitions on two data nodes, the memory usage at query completion is reduced from 6.7 MB baseline to 5.5 MB with this patch.

[codecov]

Codecov Report

Merging #4029 (494f461) into master (ae02934) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4029      +/-   ##
==========================================
- Coverage   90.70%   90.68%   -0.02%     
==========================================
  Files         214      214              
  Lines       38726    38732       +6     
==========================================
- Hits        35126    35124       -2     
- Misses       3600     3608       +8     

Impacted Files	Coverage Δ
src/chunk.h	100.00% <ø> (ø)
src/chunk.c	95.55% <100.00%> (+0.02%)	⬆️
src/planner.c	94.95% <100.00%> (+0.01%)	⬆️
src/ts_catalog/chunk_data_node.c	98.98% <100.00%> (ø)
tsl/src/fdw/modify_plan.c	90.16% <100.00%> (+0.16%)	⬆️
tsl/src/fdw/relinfo.c	96.22% <100.00%> (-0.10%)	⬇️
src/loader/bgw_launcher.c	89.50% <0.00%> (-2.47%)	⬇️
src/bgw/scheduler.c	85.67% <0.00%> (-0.88%)	⬇️
tsl/src/reorder.c	84.79% <0.00%> (-0.30%)	⬇️
tsl/src/bgw_policy/job.c	88.01% <0.00%> (-0.05%)	⬇️
... and 1 more

---

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[akuzm]

Flaky test:

     bgw_custom                   ... FAILED   305534 ms
diff -u /home/runner/work/timescaledb/timescaledb/tsl/test/expected/bgw_custom.out /home/runner/work/timescaledb/timescaledb/build/tsl/test/results/bgw_custom.out
--- /home/runner/work/timescaledb/timescaledb/tsl/test/expected/bgw_custom.out	2022-01-27 15:18:08.083515219 +0000
+++ /home/runner/work/timescaledb/timescaledb/build/tsl/test/results/bgw_custom.out	2022-01-27 15:26:09.889365828 +0000
@@ -371,6 +371,7 @@
 
 -- Delete previous jobs
 SELECT delete_job(:job_id_1);
+NOTICE:  cancelling the background worker for job 1000 (pid 11127)
  delete_job 
 ------------

[akuzm]

+ERROR: could not close pipe to external command: Broken pipe

Not sure what it is... there seems to be no core dumps.

[akuzm]

+ERROR: could not close pipe to external command: Broken pipe

Not sure what it is... there seems to be no core dumps.

Ran the tests under asan just in case, no failures.

[akuzm]

Flaky test cagg_bgw_dist_ht:

     cagg_bgw_dist_ht             ... FAILED   105330 ms
diff -u /home/runner/work/timescaledb/timescaledb/tsl/test/expected/cagg_bgw_dist_ht.out /home/runner/work/timescaledb/timescaledb/build/tsl/test/results/cagg_bgw_dist_ht.out
--- /home/runner/work/timescaledb/timescaledb/tsl/test/expected/cagg_bgw_dist_ht.out	2022-01-31 11:04:05.569033779 +0000
+++ /home/runner/work/timescaledb/timescaledb/build/tsl/test/results/cagg_bgw_dist_ht.out	2022-01-31 11:08:39.252015982 +0000
@@ -184,12 +184,11 @@
 (1 row)
 
 SELECT * FROM sorted_bgw_log;
- msg_no | mock_time |              application_name              |                                           msg                                           
---------+-----------+--------------------------------------------+-----------------------------------------------------------------------------------------
-      0 |         0 | DB Scheduler                               | [TESTING] Registered new background worker
-      1 |         0 | DB Scheduler                               | [TESTING] Wait until 25000, started at 0
-      0 |         0 | Refresh Continuous Aggregate Policy [1000] | refreshing continuous aggregate "test_continuous_agg_view" in window [ -2147483648, 6 ]
-(3 rows)
+ msg_no | mock_time | application_name |                                                msg                                                
+--------+-----------+------------------+---------------------------------------------------------------------------------------------------
+      0 |         0 | DB Scheduler     | failed to launch job 1000 "Refresh Continuous Aggregate Policy [1000]": out of background workers
+      1 |         0 | DB Scheduler     | [TESTING] Wait until 25000, started at 0
+(2 rows)