Maksytka/perf-tools
1
0
Fork 0
mirror of https://github.com/brendangregg/perf-tools.git synced 2025-12-01 07:26:04 +07:00
Code Issues Packages Projects Releases Wiki Activity

mysqld example

Browse Source
This commit is contained in:
Brendan Gregg
2015-07-02 16:36:10 -07:00
parent e2be680480
commit f3eee1f894
1 changed files with 25 additions and 0 deletions
Download Patch File Download Diff File Expand all files Collapse all files

25
examples/uprobe_example.txt
View File

@@ -161,6 +161,31 @@ The argument $retval was given a vanity name "file", which was then tested in
the filter expression "file == 0".
Here's an example of tracing the MySQL server dispatch_command() function, along
with the query string (note: the %dx register is only valid for this
architecture and this software build):
# ./uprobe 'p:dispatch_command /opt/mysql/bin/mysqld:_Z16dispatch_command19enum_server_commandP3THDPcj +0(%dx):string'
Tracing uprobe dispatch_command (p:dispatch_command /opt/mysql/bin/mysqld:0x2dbd40 +0(%dx):string). Ctrl-C to end.
mysqld-2855 [001] d... 19956674.509085: dispatch_command: (0x6dbd40) arg1="show tables"
mysqld-2855 [001] d... 19956675.541155: dispatch_command: (0x6dbd40) arg1="SELECT * FROM numbers where number > 32000"
^C
Ending tracing...
The function name, "_Z16dispatch_command19enum_server_commandP3THDPcj", is the
C++ mangled symbol.
I can name the query string argument "cmd" then test it in a filter; eg, to only
match queries that begin with "SELECT":
# ./uprobe 'p:dispatch_command /opt/mysql/bin/mysqld:_Z16dispatch_command19enum_server_commandP3THDPcj cmd=+0(%dx):string' 'cmd ~ "SELECT*"'
Tracing uprobe dispatch_command (p:dispatch_command /opt/mysql/bin/mysqld:0x2dbd40 cmd=+0(%dx):string). Ctrl-C to end.
mysqld-2855 [001] d... 19956754.619958: dispatch_command: (0x6dbd40) cmd="SELECT * FROM numbers where number > 32000"
mysqld-2855 [001] d... 19956755.060125: dispatch_command: (0x6dbd40) cmd="SELECT * FROM numbers where number > 32000"
^C
Ending tracing...
Overhead is relative to the rate of events: a higher rate of traced events,
means uprobe costs higher overhead. If you are unsure of the rate of events,
you can capture a set number only, or trace for a limited duration only (covered