By digoal
In PostgreSQL v12, after enabling the pg_stat_statements module, the lock bottleneck occurs under high concurrency. This severely degrades performance on a 104-thread machine even when pg_stat_statements.save is disabled.
perf top -ag --call-graph dwarf
Samples: 619K of event 'cpu-clock', 4000 Hz, Event count (approx.): 28398325786 lost: 446528/15917886 drop: 406385/18784766
Children Self Shared Object Symbol
- 54.20% 54.20% [kernel] [k] cpuidle_enter_state
- 5.52% 0xffffffff93a000d5
- 53.91% 0xffffffff93a59c97
0xffffffff93affc2a
0xffffffff93a37bce
- 0xffffffff93fbf9ae
53.90% 0xffffffff93fbf857
- 27.99% 0.21% postgres [.] PostgresMain
- 3.67% PostgresMain
- 13.51% 0.01% postgres [.] finish_xact_command
- 13.50% 0.02% postgres [.] CommitTransactionCommand
- 13.48% 0.05% postgres [.] CommitTransaction
- 12.45% 0.02% postgres [.] PreCommit_Portals
- 12.35% 0.01% postgres [.] PortalDrop
- 12.23% 0.01% postgres [.] PortalCleanup
- 11.76% 0.02% pg_stat_statements.so [.] pgss_ExecutorEnd
- 11.74% 0.44% pg_stat_statements.so [.] pgss_store
- 9.21% pgss_store
- 10.92% s_lock
- 11.08% 8.89% postgres [.] s_lock
8.58% ServerLoop
BackendStartup (inlined)
BackendRun (inlined)
PostgresMain
finish_xact_command
CommitTransactionCommand
CommitTransaction
PreCommit_Portals
PortalDrop
PortalCleanup
pgss_ExecutorEnd
pgss_store
s_lock
- 7.75% 0.03% postgres [.] PortalRun
- 7.57% 0.02% postgres [.] PortalRunSelect
- 7.48% 0.04% pg_stat_statements.so [.] pgss_ExecutorRun
7.44% 0.03% postgres [.] standard_ExecutorRun
- 6.65% 0.04% postgres [.] ExecScan
6.54% 0.02% postgres [.] IndexNext
6.33% 0.01% postgres [.] index_getnext_slot
+ 5.59% 0.00% [unknown] [k] 0xffffffff93a000d5
+ 5.53% 0.00% [unknown] [k] 0xffffffff93a59c97
+ 5.28% 0.00% [unknown] [k] 0xffffffff93affc2a
+ 5.28% 0.00% [unknown] [k] 0xffffffff93a37bce
Samples: 217K of event 'cpu-clock', 4000 Hz, Event count (approx.): 22185764626 lost: 411555/7098659 drop: 446791/8362859
Children Self Shared Object Symbol
- 55.76% 55.76% [kernel] [k] cpuidle_enter_state
- 7.97% 0xffffffff93a000d5
- 55.37% 0xffffffff93a59c97
0xffffffff93affc2a
0xffffffff93a37bce
0xffffffff93fbf9ae
- 29.82% 0.25% postgres [.] PostgresMain
- 4.16% PostgresMain
- 2.00% finish_xact_command
- 2.02% CommitTransactionCommand
- 2.44% CommitTransaction
- 1.90% PreCommit_Portals
- 1.83% PortalDrop
- 1.84% PortalCleanup
- 2.18% pgss_ExecutorEnd
- 10.32% pgss_store
- 10.77% s_lock
1.30% perform_spin_delay
- 1.25% exec_execute_message (inlined)
- 13.87% 0.03% postgres [.] CommitTransactionCommand
2.44% CommitTransactionCommand
- CommitTransaction
- 1.90% PreCommit_Portals
- 1.83% PortalDrop
- 1.84% PortalCleanup
- 2.18% pgss_ExecutorEnd
- 10.32% pgss_store
- 10.77% s_lock
1.30% perform_spin_delay
- 13.84% 0.04% postgres [.] CommitTransaction
- 2.40% CommitTransaction
- 1.90% PreCommit_Portals
- 1.83% PortalDrop
- 1.84% PortalCleanup
- 2.18% pgss_ExecutorEnd
- 10.32% pgss_store
- 10.77% s_lock
1.30% perform_spin_delay
- 13.58% 0.01% postgres [.] finish_xact_command
1.99% finish_xact_command
- 12.63% 0.02% postgres [.] PreCommit_Portals
- 1.87% PreCommit_Portals
- 1.83% PortalDrop
- 1.84% PortalCleanup pgbench -i -s 1000 pgbench -M prepared -n -r -P 1 -c 104 -j 104 -T 120 -S
transaction type: <builtin: select only>
scaling factor: 1000
query mode: prepared
number of clients: 104
number of threads: 104
duration: 120 s
number of transactions actually processed: 67468127
latency average = 0.185 ms
latency stddev = 0.348 ms
tps = 562224.744452 (including connections establishing)
tps = 562300.147713 (excluding connections establishing)
statement latencies in milliseconds:
0.001 \set aid random(1, 100000 * :scale)
0.185 SELECT abalance FROM pgbench_accounts WHERE aid = :aid; pgbench -M prepared -n -r -P 1 -c 104 -j 104 -T 120 -S
transaction type: <builtin: select only>
scaling factor: 1000
query mode: prepared
number of clients: 104
number of threads: 104
duration: 120 s
number of transactions actually processed: 187563515
latency average = 0.066 ms
latency stddev = 0.014 ms
tps = 1562993.591525 (including connections establishing)
tps = 1563258.811725 (excluding connections establishing)
statement latencies in milliseconds:
0.001 \set aid random(1, 100000 * :scale)
0.065 SELECT abalance FROM pgbench_accounts WHERE aid = :aid; If you detect such a problem while using PG v12, it’s better not to load the pg_stat_statements module before the community solves the problem.
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