Mysql – Mariadb MySQL Tuner report confusing

innodbmariadbMySQLmysqltuneroptimization

I'd like to ask you to clarify the report from mysqltuner regarding MariaDB database. The mysqltuner was called with –nogood flag!

 >>  MySQLTuner 1.7.1 - Major Hayden <major@mhtx.net>
 >>  Bug reports, feature requests, and downloads at http://mysqltuner.com/
 >>  Run with '--help' for additional options and output filtering

[--] Skipped version check for MySQLTuner script
[!!] Currently running unsupported MySQL version 10.0.29-MariaDB-0ubuntu0.16.04.1

-------- Log file Recommendations ------------------------------------------------------------------
[--] Log file: (0B)
[!!] Log file  doesn't exist
[!!] Log file  isn't readable.

-------- Storage Engine Statistics -----------------------------------------------------------------
[--] Status: +ARCHIVE +Aria +BLACKHOLE +CSV +FEDERATED +InnoDB +MEMORY +MRG_MyISAM +MyISAM +PERFORMANCE_SCHEMA 
[--] Data in InnoDB tables: 380M (Tables: 417)

-------- Security Recommendations ------------------------------------------------------------------
[--] There are 605 basic passwords in the list.

-------- CVE Security Recommendations --------------------------------------------------------------
[--] Skipped due to --cvefile option undefined

-------- Performance Metrics -----------------------------------------------------------------------
[--] Up for: 15s (812 q [54.133 qps], 275 conn, TX: 258K, RX: 108K)
[--] Reads / Writes: 100% / 0%
[--] Binary logging is disabled
[--] Physical Memory     : 31.3G
[--] Max MySQL memory    : 10.0G
[--] Other process memory: 1.2G
[--] Total buffers: 8.4G global + 10.7M per thread (150 max threads)
[--] P_S Max memory usage: 34M
[--] Galera GCache Max memory usage: 0B
[!!] Slow queries: 27% (221/812)
[!!] Query cache may be disabled by default due to mutex contention.
[!!] Query cache efficiency: 0.0% (0 cached / 521 selects)

-------- Performance schema ------------------------------------------------------------------------
[--] Memory used by P_S: 35.0M
[--] Sys schema isn't installed.

-------- ThreadPool Metrics ------------------------------------------------------------------------
[--] ThreadPool stat is enabled.
[--] Thread Pool Size: 8 thread(s).
[--] Using default value is good enough for your version (10.0.29-MariaDB-0ubuntu0.16.04.1)

-------- MyISAM Metrics ----------------------------------------------------------------------------
[!!] Key buffer used: 18.2% (24M used / 134M cache)
[!!] Read Key buffer hit rate: 80.0% (10 cached / 2 reads)

-------- InnoDB Metrics ----------------------------------------------------------------------------
[--] InnoDB is enabled.
[--] InnoDB Thread Concurrency: 0
[!!] Ratio InnoDB log file size / InnoDB Buffer pool size (12.5 %): 512.0M * 2/8.0G should be equal 25%
[--] InnoDB Buffer Pool Chunk Size not used or defined in your version
[!!] InnoDB Write Log efficiency: 0% (2 hits/ 0 total)

-------- AriaDB Metrics ----------------------------------------------------------------------------
[--] AriaDB is enabled.

-------- TokuDB Metrics ----------------------------------------------------------------------------
[--] TokuDB is disabled.

-------- XtraDB Metrics ----------------------------------------------------------------------------
[--] XtraDB is disabled.

-------- RocksDB Metrics ---------------------------------------------------------------------------
[--] RocksDB is disabled.

-------- Spider Metrics ----------------------------------------------------------------------------
[--] Spider is disabled.

-------- Connect Metrics ---------------------------------------------------------------------------
[--] Connect is disabled.

-------- Galera Metrics ----------------------------------------------------------------------------
[--] Galera is disabled.

-------- Replication Metrics -----------------------------------------------------------------------
[--] Galera Synchronous replication: NO
[--] No replication slave(s) for this server.
[--] This is a standalone server.

-------- Recommendations ---------------------------------------------------------------------------
General recommendations:
    MySQL started within last 24 hours - recommendations may be inaccurate
    Consider installing Sys schema from https://github.com/mysql/mysql-sys
Variables to adjust:
    query_cache_type (=0)
    query_cache_limit (> 256K, or use smaller result sets)
    innodb_log_file_size * innodb_log_files_in_group should be equals to 1/4 of buffer pool size (=4G) if possible.

What makes me confused is the "Log file Recommendations" section. I don't really know what to do with it. Then also this line:

[!!] Query cache may be disabled by default due to mutex contention.

I am also very curious why it would recommend me to change query_cache_type to 0 and increase query_cache_limit?

I'm aware that it has not been running for at least 24 hours, that's because I already adjusted the config and restarted my database. I did adjustements according to my knowledge about MariaDB, but with these few things I feel confused.

Best Answer

I can explain this line

[!!] Query cache may be disabled by default due to mutex contention.

The InnoDB storage engine and the Query Cache are in a constant state of war (See my 1.5-year-old post Why query_cache_type is disabled by default start from MySQL 5.6?)

mysqltuner is recommending setting query_cache_type to 0 so you explicitly disable the query cache. Please don't forget to set query_cache_size to 0 as well. Otherwise, the mutexing behavior will passive occur anyway.

As I said in my old post, you don't necessarily have to disable the query cache if your reasonably know the size of your most common result sets. If you can figure out that size, then you can query_cache_limit and query_cache_min_res_unit as the upper and lower bound of result set sizes. Only then can you set query_cache_type to 1.

As for your Log File Recommendations

[--] Log file: (0B)
[!!] Log file  doesn't exist
[!!] Log file  isn't readable.

Perhaps this might explain it

[!!] Currently running unsupported MySQL version 10.0.29-MariaDB-0ubuntu0.16.04.1

It is possible mysqltuner cannot relate to log files in this version of MariaDB like it does with supported versions.

Related Solutions

MySQL – Troubleshooting Startup Issues After Increasing innodb_buffer_pool_size

The two answers given from @RickJames and @drogart are essentially the remedies. (+1 for each).

Right from the error log you present, the last two lines say:

InnoDB: Error: log file ./ib_logfile0 is of different size 0 134217728 bytes

InnoDB: than specified in the .cnf file 0 268435456 bytes! `

At that point, it was evident that you set innodb_log_file_size to 256M (268435456) in my.cnf while the InnoDB Transaction Logs (ib_logfile0,ib_logfile1) were respectively 128M (134217728) each. Looking back at the link to my StackOverflow answer in your question, you had to do the following:

Step 01) Add this to my.cnf:

[mysqld]
innodb_buffer_pool_size=4G
innodb_log_file_size=1G

Step 02) Run these command in the OS

mysql -u... -p... -e"SET GLOBAL innodb_fast_shutdown = 1"
service mysql stop
rm -f /var/lib/mysql/ib_logfile*
service mysql start

So as to have confidence in what is happening, run tail -f against the error log. You will see message telling you when each innodb log file is being created.

Mysql – Perl – MySQL/MariaDB – slow with no identifiable bottleneck

Conclusion and a workaround

After exhausting all options on Windows, I decided to switch to Linux, mostly because I was frustrated with inability to profile and debug in detail.

I have moved the whole setup to Ubuntu 14.04. I first tried XAMPP but gave up because of conflicts between XAMPP and MySQL and MySQL Workbench. Then I moved to vanilla MySQL (5.5, I think) and vanilla Apache 2.

However, I was still left with the same problem – no visible bottleneck and resources still underutilized. I suspected throttling in TCP sockets (used between Perl code and MySQL), but further profiling proved this not to be the case.

Then, I turned my attantion to Perl DBI module DBD::SQL, thinking that it may be doing some throttlinig. I did some tests where I replaced DBI calls in Perl with system calls (system("mysql -e'INSERT INTO blah blah …'). I have determined that the performance did not change, therefore absolving DBI as a culprit.

I need to add one important detail now: I was in fact always running a number of my Perl scripts in parallel. Given that the CPU has 8 cores, this is necessary to utilize all of them, of course. Further debugging showed that almost all my perl processes which were supposed to work furiously were sleeping most of the time. Ubunty System Monitor shawed them as waiting on Waiting Channels wait_answer_interruptible or unix_stream_recvmsg. CPU History graph in System Monitor showed all perl processes jumping to 100% CPU utilization and then dropping to ~0% in unison. I suspected that MySQL server is not configured for multi threading, but htop showed 17 mysqld threads activated, confirming that all should be ok.
I suspected that all MySQL threads were waiting on the same semaphore and were locked out for most of the time. I dreaded delving into the dark bowels of MySQL trying to figure out what goes on inside. Instead, I decided to replace MySQL with MariaDB, even though MariaDB seems to have had the same issue originally when I was running it on Windows.

Lo and behold – this finally worked. My perl scripts were screaming.

One last problem remained: I had a very rudimentary method of parallelising the perl scripts: I would just run 10 or 20 with their respective loads and hope that they would utilize all the resources.

This has obvious drawbacks: if too many processes are spawned, the OS may spend too much time swapping them (although not a serious issue with only 20 processes, it becomes an issue with e.g. 1000). If not enough processes are spawned (e.g. less than 8, for each core) the CPU will not be utilized fully for sure. If too many processes exhaust RAM, Linux will turn to disk and will start swapping. As soon as this starts happening, everything grinds to a halt.

I searched but could not find a perl library/script/code which would spawn new processes only when CPU, memory and disk are under utilized. Hence I created my own: raspawn.pl (resource aware spawn) which I placed on github. Raspawn.pl spawns a number of processes while trying to keep resources utilization just below the maximum. It constantly checks the CPU, memory and disk utilization and only if all are less than ~90% utilized, starts a new process.

Finally, this worked. I can now process my whole load in around 7 days, instead of many months...

Best Answer

Related Solutions

MySQL – Troubleshooting Startup Issues After Increasing innodb_buffer_pool_size

Mysql – Perl – MySQL/MariaDB – slow with no identifiable bottleneck

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