MySQL over total memory allocated usage? memory leak

memoryMySQL

i'm using 5.6.21-70.0 for performance test.

when i run

mysqlslap -a –concurrency=40 –number-of-queries 1000 –iterations=500 –engine=innodb –debug-info -utest -p

do some performance test and the ram growth up over the maximum memory usage and never release

when finish mysqlslap
the memory show use 78%

i have a 1G physical memory and and i do NOT use swap

KiB Mem: 1016656 total, 953808 used, 62848 free, 30324 buffers

KiB Swap: 0 total, 0 used, 0 free. 41384 cached Mem

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
26049 mysql 20 0 1544156 778316 3992 S 16.3 76.6 6:24.01 mysqld

**it seems like mysqld use about 700M memory? why it over the max memory usage?
and why mysql never release the memory? **

my mysqlturning.pl shows:

[OK] Highest usage of available connections: 70% (42/60)

[OK] Key buffer size / total MyISAM indexes: 32.0M/98.0K

[–] Reads / Writes: 40% / 60%

[–] Total buffers: 336.0M global + 1.1M per thread (60 max threads)

[OK] Maximum possible memory usage: 403.5M (40% of installed RAM)

----------------------
BUFFER POOL AND MEMORY
----------------------
Total memory allocated 274726912; in additional pool allocated 0
Total memory allocated by read views 96
Internal hash tables (constant factor + variable factor)
    Adaptive hash index 4446416     (4425832 + 20584)
    Page hash           277432 (buffer pool 0 only)
    Dictionary cache    1170261     (1107952 + 62309)
    File system         815920  (812272 + 3648)
    Lock system         665656  (664936 + 720)
    Recovery system     0   (0 + 0)
Dictionary memory allocated 62309
Buffer pool size        16383
Buffer pool size, bytes 268419072
Free buffers            1024
Database pages          15358
Old database pages      5649
Modified db pages       0
Pending reads 0
Pending writes: LRU 0, flush list 0, single page 0
Pages made young 407, not young 484
0.00 youngs/s, 0.00 non-youngs/s
Pages read 614, created 17947, written 20737
0.00 reads/s, 0.00 creates/s, 0.00 writes/s
No buffer pool page gets since the last printout
Pages read ahead 0.00/s, evicted without access 0.00/s, Random read ahead 0.00/s
LRU len: 15358, unzip_LRU len: 0
I/O sum[0]:cur[0], unzip sum[0]:cur[0]

my my.cnf—-

 # Generated by Percona Configuration Wizard (http://tools.percona.com/) version REL5-20120208

 [mysql]

 # CLIENT #
 port                           = 3306
 socket                         = /data/data/mysql.sock

 [mysqld]

 # GENERAL #
 user                           = mysql
 default-storage-engine         = InnoDB
 socket                         = /data/data/mysql.sock
 pid-file                       = /data/data/mysql.pid
 character-set-server=utf8
 collation-server=utf8_general_ci

 # MyISAM #
 key-buffer-size                = 32M
 myisam-recover                 = FORCE,BACKUP

 # SAFETY #
 max-allowed-packet             = 16M
 max-connect-errors             = 1000000
 skip-name-resolve
 sql-mode                       = STRICT_TRANS_TABLES,ERROR_FOR_DIVISION_BY_ZERO,NO_AUTO_CREATE_USER,NO_AUTO_VALUE_ON_ZERO,NO_ENGINE_SUBSTITUTION,NO_ZERO_DATE,NO_ZERO_IN_DATE,ONLY_FULL_GROUP_BY
 sysdate-is-now                 = 1
 innodb                         = FORCE

 # DATA STORAGE #
 datadir                        = /data/data/

 # BINARY LOGGING #
 log-bin                        = /data/data/mysql-bin
 expire-logs-days               = 14
 sync-binlog                    = 1

 # CACHES AND LIMITS #
 tmp-table-size                 = 32M
 max-heap-table-size            = 32M
 query-cache-type               = 0
 query-cache-size               = 0
 max-connections                = 60
 thread-cache-size              = 50
 open-files-limit               = 65535
 table-definition-cache         = 1024
 table-open-cache               = 2048

 # INNODB #
 innodb-flush-method            = O_DIRECT
 innodb-log-files-in-group      = 2
 innodb-log-file-size           = 64M
 innodb-flush-log-at-trx-commit = 1
 innodb-file-per-table          = 1
 innodb-buffer-pool-size        = 64M

 # LOGGING #
 log-error                      = /data/data/mysql-error.log
 log-queries-not-using-indexes  = 0 # slow will not log the query which do not use index
 long-query-time                = 1
 slow-query-log                 = 1
 slow-query-log-file            = /data/data/mysql-slow.log

Best Answer

i have found out why memory leak happeneds. now i have only 1GB memory and no swap.

the performance_schema cause the allocate the memory for about 400M at startup. and innodb will take up to 400M memory usage

so，because of my.cnf use

table-definition-cache= 1024
table-open-cache= 2048 
max-connections= 60

it will cause high performance_schema allocated, more information pls see

ref1

ref2

Related Solutions

Mysql – How to debug a db memory-leak causing thesql to go before it’s own limits

...even surpassing it's theorically maximum possible allocation.

[OK] Maximum possible memory usage: 7.3G (46% of installed RAM)

There is not actually a way to calculate maximum possible memory usage for MySQL, because there is no cap on the memory it can request from the system.

The calculation done by mysqltuner.pl is only an estimate, based on a formula that doesn't take into account all possible variables, because if all possible variables were taken into account, the answer would always be "infinite." It's unfortunate that it's labeled this way.

Here is my theory on what's contributing to your excessive memory usage:

thread_cache_size       = 128

Given that your max_connections is set to 200, the value of 128 for thread_cache_size seems far too high. Here's what makes me think this might be contributing to your problem:

When a thread is no longer needed, the memory allocated to it is released and returned to the system unless the thread goes back into the thread cache. In that case, the memory remains allocated.

^{http://dev.mysql.com/doc/refman/5.6/en/memory-use.html}

If your workload causes even an occasional client thread to require a large amount of memory, those threads may be holding onto that memory, then going back to the pool and sitting around, continuing to hold on to memory they don't technically "need" any more, on the premise that holding on to the memory is less costly than releasing it if you're likely to need it again.

I think it's worth a try to do the following, after first making a note of how much memory MySQL is using at the moment.

Note how many threads are currently cached:

mysql> show status like 'Threads_cached';
+----------------+-------+
| Variable_name  | Value |
+----------------+-------+
| Threads_cached | 9     |
+----------------+-------+
1 row in set (0.00 sec)

Next, disable the thread cache.

mysql> SET GLOBAL thread_cache_size = 0;

This disables the thread cache, but the cached threads will stay in the pool until they're used one more time. Disconnect from the server, then reconnect and repeat.

mysql> show status like 'Threads_cached';

Continue disconnecting, reconnecting, and checking until the counter reaches 0.

Then, see how much memory MySQL is holding.

You may see a decrease, possibly significant, and then again you may not. I tested this on one of my systems, which had 9 threads in the cache. Once those threads had all been cleared out of the cache, the total memory held by MySQL did decrease... not by much, but it does illustrate that threads in the cache do release at least some memory when they are destroyed.

If you see a significant decrease, you may have found your problem. If you don't, then there's one more thing that needs to happen, and how quickly it can happen depends on your environment.

If the theory holds that the other threads -- the ones currently servicing active client connections -- have significant memory allocated to them, either because of recent work in their current client session or because of work requiring a lot of memory that was done by another connection prior to them languishing in the pool, then you won't see all of the potential reduction in memory consumption until those threads are allowed to die and be destroyed. Presumably your application doesn't hold them forever, but how long it will take to know for sure whether there's a difference will depend on whether you have the option of cycling your application (dropping and reconnecting the client threads) or if you'll have to just wait for them to be dropped and reconnected over time on their own.

But... it seems like a worthwhile test. You should not see a substantial performance penalty by setting thread_cache_size to 0. Fortunately, thread_cache_size is a dynamic variable, so you can freely change it with the server running.

Mysql – The total number of locks exceeds the lock table size, even after increasing buffer pool size

Try this in my.cnf file,

[mysqld] innodb_buffer_pool_size = 80M

And you need to restart the Workbench as well as the Sql service.

Best Answer

Related Solutions

Mysql – How to debug a db memory-leak causing thesql to go before it’s own limits

Mysql – The total number of locks exceeds the lock table size, even after increasing buffer pool size

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