Unexpected error "Too many connections"

Hello everyone,

my name is Roman and I need help.

In a nutshell: for the last 2 months I’ve been trying to fix issue with my application which is using Percona XtraDB Cluster 5.7. From time to time (from 1 to 10 days) mysql becomes unavailable: all new connections get error message “Too many connections”, but it looks like that mysql does nothing (low CPU usage and disk i/o). Only “kill -9” and restart of mysql server can make it available.

Below I’ll provide more details. I’ll be pleasant for any ideas what can I try to fix the issue.

Some details about my environment. I’m using Ubuntu 14.04 with Percona XtraDB Cluster 5.7:


uname -a
Linux **** 4.14.90-37 #1 SMP Tue Dec 25 17:20:38 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux


lsb_release -a
Distributor ID: Ubuntu
Description: Ubuntu 14.04.5 LTS
Release: 14.04
Codename: trusty


mysql --version
mysql Ver 14.14 Distrib 5.7.23-23, for debian-linux-gnu (x86_64) using readline 6.3


dpkg -l | grep percona
ii percona-repo-config 1.4 all Configures Percona mirror repo
ii percona-toolkit 3.0.12-1.trusty amd64 Advanced MySQL and system command-line tools
ii percona-xtrabackup-24 2.4.12-1.trusty amd64 Open source backup tool for InnoDB and XtraDB
ii percona-xtradb-cluster-client-5.7 5.7.23-31.31-2.trusty amd64 Percona XtraDB Cluster database client binaries
ii percona-xtradb-cluster-common-5.7 5.7.23-31.31-2.trusty amd64 Percona XtraDB Cluster database common files (e.g. /etc/mysql/my.cnf)
ii percona-xtradb-cluster-server-5.7 5.7.23-31.31-2.trusty amd64 Percona XtraDB Cluster database server binaries


ps uax | grep mysqld
mysql 861896 894 85.4 338018320 225641360 ? S<l Feb08 15960:03 /usr/sbin/mysqld --basedir=/usr --datadir=/var/lib/mysql-3307 --plugin-dir=/usr/lib/mysql/plugin --user=mysql --tmpdir=/var/tmp --lc-messages-dir=/usr/share/mysql --skip-external-locking --bind-address=:: --extra-port=3306 --character-set-server=utf8 --collation-server=utf8_general_ci --explicit-defaults-for-timestamp=1 --innodb-file-per-table=1 --innodb-flush-log-at-trx-commit=2 --innodb-flush-method=O_DIRECT --innodb-log-file-size=10G --slave-sql-verify-checksum=NONE --transaction-isolation=READ-COMMITTED --innodb-buffer-pool-size=192G --innodb-buffer-pool-instances=8 --innodb-checksum-algorithm=crc32 --innodb-io-capacity=5000 --innodb-io-capacity-max=5500 --innodb-log-compressed-pages=OFF --innodb-thread-concurrency=120 --innodb-flush-neighbors=0 --innodb-lru-scan-depth=256 --innodb-purge-threads=8 --innodb-page-cleaners=8 --innodb-buffer-pool-dump-at-shutdown=ON --innodb-buffer-pool-load-at-startup=ON --interactive-timeout=28800 --wait-timeout=28800 --max-allowed-packet=900M --max-connections=1000 --extra-max-connections=1000 --net-read-timeout=3600 --net-write-timeout=3600 --performance-schema-max-digest-length=10240 --thread-cache-size=200 --ft-min-word-len=1 --ft-stopword-file= --read-buffer-size=512K --read-rnd-buffer-size=1M --sort-buffer-size=1M --key-buffer-size=12G --slow-query-log=OFF --slow-query-log-file=/var/log/mysql/mysql-3307-slow.log --long-query-time=15 --binlog-cache-size=4096M --general-log=1 --general-log-file=/var/log/mysql/mysql-3307-general.log --sql-mode=NO_ENGINE_SUBSTITUTION,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_ZERO_DATE,NO_ZERO_IN_DATE --replicate-ignore-db=performance_schema --replicate-ignore-db=information_schema --binlog-format=ROW --binlog-ignore-db=mysql --expire-logs-days=1 --enforce-gtid-consistency=ON --gtid-mode=Off --log-bin=/var/log/mysql/mysql-3307-bin.log --max-binlog-files=500 --relay-log=/var/log/mysql/mysqld-3307-relay-bin --server-id=307 --log-error=/var/log/mysql/mysql-3307-error.log --pid-file=/var/run/mysqld/mysqld-3307.pid --socket=/var/run/mysqld/mysqld-3307.sock --port=3307 --wsrep_start_position=00000000-0000-0000-0000-000000000000:-1


SELECT VERSION();
5.7.23-23-57-log

Several words about my application and data. I have PHP based application which is working with 5 mysql shards. Shards are independent on each other. Each shard have master-slave replication to backup server. So, I have 10 servers: 5 masters and 5 replicas. Application is working only with master servers, once a day special cron task takes a backup from each replica by using Percona XtraBackup.

My mysql-servers are very powerful:


lscpu
Architecture: x86_64
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Little Endian
CPU(s): 56
...


cat /proc/meminfo
MemTotal: 264019652 kB
MemFree: 2619616 kB
MemAvailable: 32820228 kB
Buffers: 920 kB
Cached: 31100868 kB
SwapCached: 0 kB
...


df -h
Filesystem Size Used Avail Use% Mounted on
udev 126G 4.0K 126G 1% /dev
tmpfs 26G 16M 26G 1% /run
/dev/md0 32G 5.2G 27G 17% /
none 4.0K 0 4.0K 0% /sys/fs/cgroup
none 5.0M 0 5.0M 0% /run/lock
none 126G 28K 126G 1% /run/shm
none 100M 0 100M 0% /run/user
/dev/md2 1.8T 1.3T 505G 72% /srv/local
tmpfs 128M 4.0K 128M 1% /var/tmp/skynet/cqudp

Data is located in /srv/local partition, there are enough room for the data on this partition.

My databases are big: each shard have size ~500 Gb. There are about 50 tables in my DBs, but only several of them contains almost all data. All shards have roughly speaking the same size, the same number of requests, the same number of clients. One important fact: I faced my issue only on one shard.

My application is using a concept of “workers”. Worker is a short php-program which usually working in the following way:

  1. start and establish connection to mysql-server,
  2. get some data from DB,
  3. get some data from external API,
  4. do some calculations and put data back to DB,
  5. close connection to DB.

In common case I have not more than 200 workers working with each shard and I have max_connections variable in mysql-server set to value 1000. In common case it’s much more then enough to work wihout any issues. Workers are usually working very fast: some of them can do their job during several seconds, but some of them can work during minutes or even dozens of minutes. Usually I have hundreds workers starts and finishes per every minute.

Most part of queries made by workers are UPDATEs. I have a monitoring based on Percona’s script https://github.com/percona/percona-monitoring-plugins/blob/master/cacti/scripts/ss_get_mysql_stats.php, here is screenshot from it:

When I faced issue with “Too many connections error” I checked that I didn’t have more workers then usual. No one besides workers can connect to DB. First of all I tried to optimize my application and separate queries which update a lot of data to smaller queries and distribute them in time. It didn’t help.

Then I tried to compare settings between all my DB servers and found, that problem server has default value of variable binlog_cache_size - 32Kb, whereas on other servers this variable have value 100Mb. Then I also found that value of binlog cache usage is enormous on problem server - millions per day, whereas on other servers it’s something like couple of thousands each day.

When I set binlog_cache_size to 100 Mb on problem server it was working without problems for 10 days, before that it was working not longer then 2-3 days. But after 10 days it again becames unavailable with the message “Too many connections”. I also noticed that when mysql-server starts serving error “Too many connections” it’s extensively using CPU and doing lot of writes on disk. But after couple of minutes CPU usage and i/o goes down almost to 0, but mysq still serving error “Too many connections”.

I have logs from atop utility, which allows to log system state every minute. Below you can find a couple of screenshots made at the moment of error starts at 10:33.



I didn’y have general log enabled on my problem server and I decided to enable it (writing data to file) in hope to find something interesting in it at the moment of error “Too many connections” begins. I haven’t found anything yet in this log, but my mysql server broke down twise during 2 days I enabled this log. Looks like there too many disk i/o operation and this might be a reason of error. I have these SSDs in my server: https://www.micron.com/products/solid-state-drives/product-lines/5100 and I found that they can deal with up to 500 Mb/s of writes and 43000 iops. Look like I didn’t reach these limits in my case.

Does anyone has any ideas what should I try to find and fix the reason of issues with my DB server?

Additional information about settings of my server:

I suspect we may need more data but first point to check is when you hit issue due to see flow control. Can you share output of “show processlist” and show status like ‘wsrep%’
It would be great to run pt-pmp (check percona toolkit) to get trace of what each thread is doing.

You can also check pt-stalk that can help collect most of the needed params https://www.percona.com/doc/percona-toolkit/LATEST/pt-stalk.html

Hello, krunalbauskar,

thank you for your answer. I’ll definitely try your advice and run these 2 queries and pt-pmp utility when I meet my issue next time and than I publish results here.

I’ll also set up pt-stalk to collect additional information. I have one additional question about pt-stalk setup. As far as I understood from docs in my case I should run it somehow like this:

pt-stalk --daemonize --ask-pass --collect-tcpdump --sleep=3600 --threshold=1000 --variable=Threads_running --user=myuser --host=myhost --cycles=5

But the problem is that in time when I have “Too many connections” error values of “Threads_running” and other related counters are not high. Here is screenshot from the last outage:
I don’t know if it just monitoring tool can’t collect data because of outage, or it’s a real values. Is it worth setting trigger on “Max_used_connections” variable? Something like this:

pt-stalk --daemonize --ask-pass --collect-tcpdump --sleep=3600 --threshold=1000 --variable=Max_used_connections --user=myuser --host=myhost --cycles=5

Many thanks for your help!

Hi Roman,

You have gaps in your graphs, which likely means the monitoring agent could already not connect to the database due to the problem with avaialble connections.
To avoid that, configure an extra TCP port for your database instances and use that one for monitoring as well as for pt-stalk itself.
Check here: https://www.percona.com/doc/percona-server/LATEST/performance/threadpool.html#extra_port

For pt-stalk in this case, I’d rather use something like --threshold=400 --variable=Threads_connected

Hello przemek,

thank you, you are right, I’m using the same port for application and monitoring. I’ll fix it.

Hello everyone,

today my DB again became unavailable with “Too many connections” error. And what is suspicious - last time this problem happened exactly 10 days ago. And previous outage (with the same DB settings) also was 10 days before.

Unfortunately pt-stalk didn’t collect any data, maybe because I set threshold to 900, now I decreased it to 400:

--threshold=400 --variable=Threads_connected

But pt-pmp utility collected some data. Here is pt-pmp output when my server is working properly: https://pastebin.com/raw/iA1chWsk

And here is pt-pmp output 20 minutes after the problem happened:


root@***:~# pt-pmp
Wed Feb 20 18:07:46 MSK 2019
654 __lll_lock_wait(libpthread.so.0),_L_lock_1081(libpthread.so.0),pthread_mutex_lock(libpthread.so.0),THD::init,THD::THD,Channel_info::create_thd,Channel_info_tcpip_socket::create_thd,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
80 pthread_cond_wait,Stage_manager::enroll_for,MYSQL_BIN_LOG::change_stage,MYSQL_BIN_LOG::ordered_commit,MYSQL_BIN_LOG::commit,ha_commit_trans,trans_commit_stmt,mysql_execute_command,mysql_parse,::??,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
28 pthread_cond_wait,os_event::wait_low,lock_wait_suspend_thread,row_mysql_handle_errors,row_search_mvcc,ha_innobase::index_read,handler::ha_index_read_map,::??,sub_select,JOIN::exec,handle_query,::??,mysql_execute_command,mysql_parse,::??,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
17 __lll_lock_wait(libpthread.so.0),_L_lock_1081(libpthread.so.0),pthread_mutex_lock(libpthread.so.0),Global_THD_manager::remove_thd,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
10 libaio::??(libaio.so.1),LinuxAIOHandler::collect,LinuxAIOHandler::poll,os_aio_handler,fil_aio_wait,io_handler_thread,start_thread(libpthread.so.0),clone(libc.so.6)
9 pthread_cond_wait,Stage_manager::enroll_for,MYSQL_BIN_LOG::change_stage,MYSQL_BIN_LOG::ordered_commit,MYSQL_BIN_LOG::commit,ha_commit_trans,trans_commit,mysql_execute_command,mysql_parse,::??,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
8 nanosleep(libpthread.so.0),os_thread_sleep,buf_lru_manager,start_thread(libpthread.so.0),clone(libc.so.6)
7 pthread_cond_wait,os_event::wait_low,srv_worker_thread,start_thread(libpthread.so.0),clone(libc.so.6)
7 pthread_cond_wait,os_event::wait_low,buf_flush_page_cleaner_worker,start_thread(libpthread.so.0),clone(libc.so.6)
7 poll(libc.so.6),vio_io_wait,vio_socket_io_wait,vio_read,::??,::??,my_net_read,Protocol_classic::read_packet,Protocol_classic::get_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
2 __lll_lock_wait(libpthread.so.0),_L_lock_1081(libpthread.so.0),pthread_mutex_lock(libpthread.so.0),Global_THD_manager::do_for_all_thd_copy,fill_schema_processlist,::??,get_schema_tables_result,JOIN::prepare_result,JOIN::exec,handle_query,::??,mysql_execute_command,mysql_parse,::??,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 sigwait(libpthread.so.0),signal_hand,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 sigwaitinfo(libc.so.6),::??,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_wait,os_event::wait_low,srv_purge_coordinator_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_wait,os_event::wait_low,buf_resize_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_wait,os_event::wait_low,buf_dump_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_wait,compress_gtid_table,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_timedwait,os_event::timed_wait,os_event::wait_time_low,srv_monitor_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_timedwait,os_event::timed_wait,os_event::wait_time_low,srv_error_monitor_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_timedwait,os_event::timed_wait,os_event::wait_time_low,lock_wait_timeout_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_timedwait,os_event::timed_wait,os_event::wait_time_low,ib_wqueue_timedwait,fts_optimize_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_timedwait,os_event::timed_wait,os_event::wait_time_low,dict_stats_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_timedwait,os_event::timed_wait,os_event::wait_time_low,buf_flush_page_cleaner_coordinator,start_thread(libpthread.so.0),clone(libc.so.6)
1 pthread_cond_timedwait,MYSQL_BIN_LOG::wait_for_update_bin_log,Binlog_sender::send_binlog,Binlog_sender::run,mysql_binlog_send,com_binlog_dump,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 poll(libc.so.6),Mysqld_socket_listener::listen_for_connection_event,mysqld_main,__libc_start_main(libc.so.6),_start
1 nanosleep(libpthread.so.0),os_thread_sleep,srv_master_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 __lll_lock_wait(libpthread.so.0),_L_lock_909(libpthread.so.0),pthread_mutex_lock(libpthread.so.0),PolyLock_lock_log::rdlock,sys_var::value_ptr,get_one_variable_ext,System_variable::init,PFS_system_variable_cache::do_materialize_all,table_session_variables::rnd_init,ha_perfschema::rnd_init,handler::ha_rnd_init,init_read_record,join_init_read_record,sub_select,JOIN::exec,TABLE_LIST::materialize_derived,join_materialize_derived,QEP_TAB::prepare_scan,sub_select,JOIN::exec,handle_query,::??,mysql_execute_command,mysql_parse,::??,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 __lll_lock_wait(libpthread.so.0),_L_lock_909(libpthread.so.0),pthread_mutex_lock(libpthread.so.0),::??,MYSQL_BIN_LOG::ordered_commit,MYSQL_BIN_LOG::commit,ha_commit_trans,trans_commit,mysql_execute_command,mysql_parse,::??,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 __lll_lock_wait(libpthread.so.0),_L_lock_909(libpthread.so.0),pthread_mutex_lock(libpthread.so.0),::??,MYSQL_BIN_LOG::new_file_impl,MYSQL_BIN_LOG::rotate,MYSQL_BIN_LOG::ordered_commit,MYSQL_BIN_LOG::commit,ha_commit_trans,trans_commit_stmt,mysql_execute_command,mysql_parse,::??,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 __lll_lock_wait(libpthread.so.0),_L_lock_909(libpthread.so.0),pthread_mutex_lock(libpthread.so.0),MYSQL_BIN_LOG::change_stage,MYSQL_BIN_LOG::ordered_commit,MYSQL_BIN_LOG::commit,ha_commit_trans,trans_commit_stmt,mysql_execute_command,mysql_parse,::??,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 __lll_lock_wait(libpthread.so.0),_L_lock_1081(libpthread.so.0),pthread_mutex_lock(libpthread.so.0),THD::init,THD::THD,Channel_info::create_thd,Channel_info_local_socket::create_thd,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 __lll_lock_wait(libpthread.so.0),_L_lock_1081(libpthread.so.0),pthread_mutex_lock(libpthread.so.0),Log_in_use::operator,Global_THD_manager::do_for_all_thd,MYSQL_BIN_LOG::purge_logs_maximum_number,MYSQL_BIN_LOG::purge,MYSQL_BIN_LOG::ordered_commit,MYSQL_BIN_LOG::commit,ha_commit_trans,trans_commit_stmt,mysql_execute_command,mysql_parse,::??,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)
1 __lll_lock_wait(libpthread.so.0),_L_lock_1081(libpthread.so.0),pthread_mutex_lock(libpthread.so.0),Fill_process_list::operator,Global_THD_manager::do_for_all_thd_copy,fill_schema_processlist,::??,get_schema_tables_result,JOIN::prepare_result,JOIN::exec,handle_query,::??,mysql_execute_command,mysql_parse,::??,dispatch_command,do_command,handle_connection,pfs_spawn_thread,start_thread(libpthread.so.0),clone(libc.so.6)

Does anyone have any ideas what can I try to do to catch and fix this bug?

I also collected some data from atop logs. Here is atop log at the moment of outage:

ATOP - *** 2019/02/20 17:48:06 ---------P-/- 1m0s elapsed
PRC | sys 39.92s | user 12m29s | | | #proc 692 | #trun 27 | #tslpi 915 | #tslpu 10 | #zombie 0 | clones 3859 | | | #exit 1555 |
CPU | sys 72% | user 1251% | irq 17% | | | idle 4129% | wait 132% | | steal 0% | guest 0% | | curf 2.49GHz | curscal 77% |
CPL | avg1 22.59 | | avg5 18.27 | avg15 15.91 | | | csw 5468160 | | intr 6275899 | | | numcpu 56 | |
MEM | tot 251.8G | free 978.1M | cache 28.1G | dirty 299.6M | buff 0.8M | slab 1.0G | slrec 824.8M | shmem 16.0M | shrss 0.0M | shswp 0.0M | vmbal 0.0M | hptot 0.0M | hpuse 0.0M |
SWP | tot 4.0G | free 4.0G | | | | | | | | | vmcom 545.4G | | vmlim 129.9G |
PAG | scan 32206 | steal 32206 | | stall 0 | | | | | | | swin 0 | | swout 0 |
MDD | md0 | busy 0% | | read 1122 | write 43 | KiB/r 69 | KiB/w 22 | | MBr/s 1.3 | MBw/s 0.0 | avq 0.00 | | avio 0.00 ms |
MDD | md2 | busy 0% | | read 7084 | write 149222 | KiB/r 108 | KiB/w 92 | | MBr/s 12.6 | MBw/s 223.5 | avq 0.00 | | avio 0.00 ms |
DSK | sdb | busy 48% | | read 1860 | write 69289 | KiB/r 55 | KiB/w 50 | | MBr/s 1.7 | MBw/s 56.8 | avq 49.06 | | avio 0.41 ms |
DSK | sdd | busy 46% | | read 1799 | write 70242 | KiB/r 57 | KiB/w 49 | | MBr/s 1.7 | MBw/s 57.1 | avq 32.42 | | avio 0.38 ms |
DSK | sdc | busy 42% | | read 1810 | write 70641 | KiB/r 56 | KiB/w 49 | | MBr/s 1.7 | MBw/s 57.1 | avq 32.76 | | avio 0.35 ms |
NET | transport | tcpi 308618 | tcpo 660798 | udpi 318 | udpo 479 | tcpao 290 | tcppo 1551 | | tcprs 262 | tcpie 0 | tcpor 312 | udpnp 0 | udpie 0 |
NET | network | ipi 310601 | | ipo 306791 | ipfrw 0 | deliv 310601 | | | | | icmpi 856 | | icmpo 1595 |
NET | eth0 5% | pcki 325816 | pcko 661878 | sp 10 Gbps | si 81 Mbps | so 558 Mbps | | coll 0 | mlti 6 | erri 0 | erro 0 | drpi 0 | drpo 0 |
NET | lo ---- | pcki 1205 | pcko 1205 | sp 0 Mbps | si 206 Kbps | so 206 Kbps | | coll 0 | mlti 0 | erri 0 | erro 0 | drpi 0 | drpo 0 |

PID TID RUID EUID THR SYSCPU USRCPU VGROW RGROW RDDSK WRDSK ST EXC S CPUNR CPU CMD 1/1
713711 - mysql mysql 267 26.42s 12m11s -4.0G 60000K 361.0M 6.4G -- - S 16 1264% mysqld
712628 - root root 1 0.00s 0.00s 0K 0K 0K 0K -- - S 16 0% mysqld_safe

atop log 20 minutes after outage:

ATOP - *** 2019/02/20 18:07:06 ---------P-/- 1m0s elapsed
PRC | sys 8.60s | user 13.07s | | | #proc 682 | #trun 1 | #tslpi 1540 | #tslpu 0 | #zombie 0 | clones 3055 | | | #exit 678 |
CPU | sys 16% | user 22% | irq 1% | | | idle 5562% | wait 0% | | steal 0% | guest 0% | | curf 2.59GHz | curscal 81% |
CPL | avg1 0.28 | | avg5 1.56 | avg15 6.91 | | | csw 1641770 | | intr 123694 | | | numcpu 56 | |
MEM | tot 251.8G | free 1.7G | cache 18.5G | dirty 0.3M | buff 0.8M | slab 925.6M | slrec 742.9M | shmem 16.2M | shrss 0.0M | shswp 0.0M | vmbal 0.0M | hptot 0.0M | hpuse 0.0M |
SWP | tot 4.0G | free 4.0G | | | | | | | | | vmcom 621.6G | | vmlim 129.9G |
MDD | md0 | busy 0% | | read 0 | write 2 | KiB/r 0 | KiB/w 256 | | MBr/s 0.0 | MBw/s 0.0 | avq 0.00 | | avio 0.00 ms |
MDD | md2 | busy 0% | | read 0 | write 170 | KiB/r 0 | KiB/w 12 | | MBr/s 0.0 | MBw/s 0.0 | avq 0.00 | | avio 0.00 ms |
DSK | sdd | busy 0% | | read 0 | write 267 | KiB/r 0 | KiB/w 6 | | MBr/s 0.0 | MBw/s 0.0 | avq 1.00 | | avio 0.30 ms |
DSK | sdc | busy 0% | | read 0 | write 281 | KiB/r 0 | KiB/w 5 | | MBr/s 0.0 | MBw/s 0.0 | avq 1.00 | | avio 0.09 ms |
DSK | sda | busy 0% | | read 6 | write 248 | KiB/r 2 | KiB/w 6 | | MBr/s 0.0 | MBw/s 0.0 | avq 1.00 | | avio 0.08 ms |
NET | transport | tcpi 2344 | tcpo 2322 | udpi 307 | udpo 453 | tcpao 454 | tcppo 89 | | tcprs 181 | tcpie 0 | tcpor 152 | udpnp 0 | udpie 0 |
NET | network | ipi 4274 | | ipo 4521 | ipfrw 0 | deliv 4274 | | | | | icmpi 1004 | | icmpo 1566 |
NET | eth0 0% | pcki 2993 | pcko 2862 | sp 10 Gbps | si 1333 Kbps | so 813 Kbps | | coll 0 | mlti 7 | erri 0 | erro 0 | drpi 0 | drpo 0 |
NET | lo ---- | pcki 1296 | pcko 1296 | sp 0 Mbps | si 28 Kbps | so 28 Kbps | | coll 0 | mlti 0 | erri 0 | erro 0 | drpi 0 | drpo 0 |

PID TID RUID EUID THR SYSCPU USRCPU VGROW RGROW RDDSK WRDSK ST EXC S CPUNR CPU CMD 1/1
713711 - mysql mysql 839 0.00s 0.06s 5460K 248K 0K 0K -- - S 14 0% mysqld
712628 - root root 1 0.00s 0.00s 0K 0K 0K 0K -- - S 16 0% mysqld_safe


I don’t know is it vital or not, but my libc version is:


dpkg -l | grep libc-bin
ii libc-bin 2.19-0ubuntu6.13 amd64 Embedded GNU C Library: Binaries

Looks like I faced this bug: https://jira.percona.com/browse/PS-4716. I’ll try to upgrade mysql to 5.7.25.

Did upgrading resolve your issue?

I updated my DB only 2 days ago and now need to wait at least 3-4 weeks to make any conclusions, because even previous version of DB could work up to 10 days.

Does anyone knows if the field “Affects Version/s:” in Percona’s Jira contain exact list of affected versions or approximate list?

In the issue https://jira.percona.com/browse/PS-4716 field “Affected versions” contains values “5.7.22-22, 5.7.23-23”. Before my DB was updated to 5.7.23 it had version 5.7.21 and I want to know if this version also had this bug or it was introduced in 5.7.22.

Hello everyone,

more then 2 weeks passed from the moment I upgraded my mysql server from 5.7.23 to 5.7.25 (I’d done it at 25.02.2019). From that time server didn’t have “Too many connections” error, looks like this upgrade fixed the issue. But unfortunately this upgrade dramatically decreased performance, value of innodb row lock time increased significantly:

Does someone have any ideas what can I check to fix this performance issue?

Some of my variables: