# SEMAPHORES - S-lock & X-lock on RW-latch **URL:** \ **Category:** Percona Server for MySQL 5.6\ **Created:** [April 9, 2019, 5:47am UTC](https://forums.percona.com/t/semaphores-s-lock-x-lock-on-rw-latch/6957 "2019-04-09T05:47:30Z")\ **Posts on this page:** 4\ **Page:** 1
**Author:** ![pooja.gupta](https://avatars.discourse-cdn.com/v4/letter/p/258eb7/32.png) [@pooja.gupta](https://forums.percona.com/u/pooja.gupta)\ **Post date:** [April 9, 2019, 5:47am UTC](https://forums.percona.com/t/semaphores-s-lock-x-lock-on-rw-latch/6957/1 "2019-04-09T05:47:30Z")
I can see many types of contention in the show engine innodb status\G Its increasing load on the server , CPU utilization was High and High I/O noticed. Can see below contentions in error logs. * * * ## SEMAPHORES OS WAIT ARRAY INFO: reservation count 197682819 –Thread 139909836908288 has waited at btr0cur.cc line 591 for 0.0000 seconds the semaphore: S-lock on RW-latch at 0x7f3eb0029fa0 ‘&new\_index-\>lock’ a writer (thread id 139911101409024) has reserved it in mode exclusive number of readers 0, waiters flag 1, lock\_word: 0 Last time read locked in file btr0cur.cc line 591 Last time write locked in file /mnt/workspace/percona-server-5.6-redhat-binary/label\_exp/centos7-64/rpmbuild/BUILD/percona-server-5.6.39-83.1/storage/innobase/btr/btr0cur.cc line 582 OS WAIT ARRAY INFO: reservation count 197784171 –Thread 139909319145216 has waited at btr0sea.cc line 1494 for 0.0000 seconds the semaphore: X-lock on RW-latch at 0x23d9658 ‘&btr\_search\_latch\_arr[i]’ a writer (thread id 139909794551552) has reserved it in mode exclusive number of readers 0, waiters flag 0, lock\_word: 0 Last time read locked in file btr0sea.cc line 954 Last time write locked in file /mnt/workspace/percona-server-5.6-redhat-binary/label\_exp/centos7-64/rpmbuild/BUILD/percona-server-5.6.39-83.1/storage/innobase/btr/btr0sea.cc line 1494 OS WAIT ARRAY INFO: reservation count 202249793 –Thread 139909786564352 has waited at btr0pcur.cc line 467 for 0.0000 seconds the semaphore: S-lock on RW-latch at 0x7f41132df320 ‘&block-\>lock’ a writer (thread id 139909862520576) has reserved it in mode wait exclusive number of readers 1, waiters flag 1, lock\_word: ffffffffffffffff Last time read locked in file row0sel.cc line 3346 Last time write locked in file /mnt/workspace/percona-server-5.6-redhat-binary/label\_exp/centos7-64/rpmbuild/BUILD/percona-server-5.6.39-83.1/storage/innobase/row/row0row.cc line 823 –Thread 139909849413376 has waited at row0sel.cc line 3346 for 0.0000 seconds the semaphore: S-lock on RW-latch at 0x7f41132df320 ‘&block-\>lock’ a writer (thread id 139909862520576) has reserved it in mode wait exclusive number of readers 1, waiters flag 1, lock\_word: ffffffffffffffff Last time read locked in file row0sel.cc line 3346 Last time write locked in file /mnt/workspace/percona-server-5.6-redhat-binary/label\_exp/centos7-64/rpmbuild/BUILD/percona-server-5.6.39-83.1/storage/innobase/row/row0row.cc line 823 –Thread 139909836089088 has waited at row0sel.cc line 3346 for 0.0000 seconds the semaphore: S-lock on RW-latch at 0x7f406d31ed20 ‘&block-\>lock’ number of readers 1, waiters flag 0, lock\_word: fffff Last time read locked in file row0sel.cc line 3346 Last time write locked in file /mnt/workspace/percona-server-5.6-redhat-binary/label\_exp/centos7-64/rpmbuild/BUILD/percona-server-5.6.39-83.1/storage/innobase/row/row0ins.cc line 2718 –Thread 139909854123776 has waited at buf0buf.cc line 3303 for 0.0000 seconds the semaphore: Mutex at 0x7f40a4ad8840 ‘&block-\>mutex’, lock var 0 waiters flag 0 –Thread 139909777962752 has waited at btr0sea.cc line 1380 for 0.0000 seconds the semaphore: S-lock on RW-latch at 0x23d9658 ‘&btr\_search\_latch\_arr[i]’ number of readers 4, waiters flag 0, lock\_word: ffffc Last time read locked in file btr0sea.cc line 954 –Thread 139909845509888 has waited at btr0pcur.cc line 467 for 0.0000 seconds the semaphore: S-lock on RW-latch at 0x7f41132df320 ‘&block-\>lock’ a writer (thread id 139909862520576) has reserved it in mode wait exclusive number of readers 1, waiters flag 1, lock\_word: ffffffffffffffff Last time read locked in file row0sel.cc line 3346 Last time write locked in file /mnt/workspace/percona-server-5.6-redhat-binary/label\_exp/centos7-64/rpmbuild/BUILD/percona-server-5.6.39-83.1/storage/innobase/row/row0row.cc line 823 Mysql version is 5.6.39-83.1 Do i need to set innodb\_thread\_concurrency to some value, currently its innodb\_thread\_concurrency =0, innodb\_buffer\_pool\_instances =1, innodb\_read\_io\_threads=64, innodb\_write\_io\_threads=64, innodb\_adaptive\_hash\_index=ON. All tables are innodb . Buffer pool size is 80GB. Total memory on the servers is 125GB and 8 core’s CPU ---
**Author:** ![pooja.gupta](https://avatars.discourse-cdn.com/v4/letter/p/258eb7/32.png) [@pooja.gupta](https://forums.percona.com/u/pooja.gupta)\ **Post date:** [April 10, 2019, 8:45pm UTC](https://forums.percona.com/t/semaphores-s-lock-x-lock-on-rw-latch/6957/2 "2019-04-10T20:45:11Z")
Hi, Do I need to adjust below parameters ? ±--------------------------±------+ | Variable\_name | Value | ±--------------------------±------+ | innodb\_thread\_concurrency | 0 | ±--------------------------±------+ ±-----------------------±------+ | Variable\_name | Value | ±-----------------------±------+ | innodb\_read\_io\_threads | 64 | ±-----------------------±------+ ±------------------------±------+ | Variable\_name | Value | ±------------------------±------+ | innodb\_write\_io\_threads | 64 | ±------------------------±------+ ±--------------------------------------±------+ | Variable\_name | Value | ±--------------------------------------±------+ | innodb\_adaptive\_hash\_index | ON | ±--------------------------------------±------+ ±-----------------------------±------+ | Variable\_name | Value | ±-----------------------------±------+ | innodb\_buffer\_pool\_instances | 1 | ±-----------------------------±------+ Looking for expert opinion, Any help will be appreciated. Thanks, Pooja. ---
**Author:** ![bowenzhuang](https://avatars.discourse-cdn.com/v4/letter/b/ea5d25/32.png) [@bowenzhuang](https://forums.percona.com/u/bowenzhuang)\ **Post date:** [June 29, 2020, 2:32am UTC](https://forums.percona.com/t/semaphores-s-lock-x-lock-on-rw-latch/6957/3 "2020-06-29T02:32:01Z")
i also encountered the same problem in mysql 5.6.40 .  Looking for expert opinion, Any help will be appreciated. +1  ---
**Author:** ![vaibhav\_upadhyay40](https://sea1.discourse-cdn.com/flex019/user_avatar/forums.percona.com/vaibhav_upadhyay40/32/9_2.png) [@vaibhav\_upadhyay40](https://forums.percona.com/u/vaibhav_upadhyay40)\ **Post date:** [July 1, 2020, 4:48pm UTC](https://forums.percona.com/t/semaphores-s-lock-x-lock-on-rw-latch/6957/4 "2020-07-01T16:48:37Z")
Hi @bowenzhuang and @“pooja.gupta” Check hash and non-hash search in innodb engine output. If its ok to test in your environment to disable innodb\_adaptive\_hash\_index, please do so and monitor for the performance and for the above issue. @“pooja.gupta” apart from this, i would recommend to split the buffer pool into multiple instances.  Hope this helps.