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Displaying posts with tag: valgrind (reset)

MySQL QA Episode 11: Valgrind Testing: Pro’s, Con’s, Why and How
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Today’s episode is all about Valgrind – from the pro’s to the con’s, from the why to the how! This episode will be of interest to anyone who is or wants to work with Valgrind on a regular or semi-regular basis.

  1. Pro’s/Why
  2. Con’s
  3. How
    1. Using the latest version
      sudo [yum/apt-get] install valgrind
      #OR#
      sudo [yum/apt-get] remove valgrind
      sudo [yum/apt-get] install bzip2 glibc*
      wget http://valgrind.org/downloads/valgrind-3.10.1.tar.bz2
      tar -xf valgrind-3.10.1.tar.bz2; cd valgrind-3.10.1







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Helgrind and MySQL 5.7
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Valgrind's helgrind tool identifies data races and lock deadlocks in multi-threaded programs.  Since the MySQL server is a multi-threaded program, can helgrind find any issues in the MySQL server?

A simple test that does nothing except start up the MySQL server and shut it down is run on the MySQL test suite with  …

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Why TokuDB does not use the ‘uint3korr’ function
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The ‘uint3korr’ function inside of the mysqld server extracts a 3 byte unsigned integer from a memory buffer. One use is for ‘mediumint’ columns which encode their value in 3 bytes. MySQL 5.6 and MariaDB 10.0 claims to have optimized this function for x86 and x86_64 processors. There is a big comment that says:

Attention: Please, note, uint3korr reads 4 bytes (not 3)!
It means, that you have to provide enough allocated space.

The ‘uint3korr’ optimization may be fast, but it is not valgrind safe. Here is an example where valgrind detects TokuDB reading beyond the end of a buffer when it uses the ‘uint3korr’ function. …

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Uninitialized data in the TokuDB recovery log
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A TokuDB MySQL test run with valgrind reported an uninitialized data error when writing into the TokuDB recovery log.

==1032== Syscall param write(buf) points to uninitialised byte(s)
==1032== at 0x3EFA60E4ED: ??? (in /lib64/libpthread-2.12.so)
==1032== by 0xB894038: toku_os_full_write(int, void const*, unsigned long) (file.cc:249)
==1032== by 0xB83248A: write_outbuf_to_logfile(tokulogger*, __toku_lsn*) (logger.cc:513)
==1032== by 0xB83326C: toku_logger_maybe_fsync(tokulogger*, __toku_lsn, int, bool) (logger.cc:836)
==1032== by 0xB8327DE: toku_logger_fsync_if_lsn_not_fsynced(tokulogger*, __toku_lsn) (logger.cc:586)
==1032== by 0xB8493E6: …
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Copying unused bytes is bad (duh!)
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Last summer my colleague Marko Mäkelä committed this seemingly innocent performance fix for InnoDB in MySQL 5.6:

3581 Marko Makela    2011-08-10
Bug#12835650 VARCHAR maximum length performance impact

row_sel_field_store_in_mysql_format(): Do not pad the unused part of
the buffer reserved for a True VARCHAR column (introduced in 5.0.3).
Add Valgrind instrumentation ensuring that the unused part will be
flagged uninitialized.
Before this, buffers which were used to send VARCHARs from InnoDB to the MySQL server were padded with 0s if the string was shorter than specified by …








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An exercise on using valgrind with MySQL on MacOSX
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Valgrind is a very useful tool. This has been recognized by the mysql developers long ago. They've even invested effort into creating a special mode for the mysql test driver (mysql-test-run.pl) to invoke the server tests under valgrind and collect the results.
But the sad fact remains that this is not exactly usable on MacOSX due to immaturity of the valgrind's support for this platform.
Encouraged by the announcement of the return of MacOSX support in valgrind 3.6 I've started periodically giving a try to the latest valgrind version out of the …

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An exercise on using valgrind with MySQL on MacOSX
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An exercise on using valgrind with MySQL on MacOSX
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An exercise on using valgrind with MySQL on MacOSX
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Debugging memory leaks in plugins with Valgrind
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I had an interesting IRC discussion the other day with Monty Taylor about what turned out to be a limitation in Valgrind with respect to debugging memory leaks in dynamically loaded plugins.

Monty Taylor's original problem was with Drizzle, but as it turns out, it is common to all of the MySQL-derived code bases. When there is a memory leak from an allocation in a dynamically loaded plugin, Valgrind will detect the leak, but the part of the stack trace that is within the plugin shows up as an unhelpful three question marks "???":

==1287== 400 bytes in 4 blocks …
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