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d602d6b Aug 2, 2016
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Demonstrations of mysqld_qslower, the Linux eBPF/bcc version.
mysqld_qslower traces queries served by a MySQL server, and prints those that
exceed a latency (query time) threshold. By default a threshold of 1 ms is
used. For example:
# ./mysqld_qslower.py `pgrep -n mysqld`
Tracing MySQL server queries for PID 14371 slower than 1 ms...
TIME(s) PID MS QUERY
0.000000 18608 130.751 SELECT * FROM words WHERE word REGEXP '^bre.*n$'
2.921535 18608 130.590 SELECT * FROM words WHERE word REGEXP '^alex.*$'
4.603549 18608 24.164 SELECT COUNT(*) FROM words
9.733847 18608 130.936 SELECT count(*) AS count FROM words WHERE word REGEXP '^bre.*n$'
17.864776 18608 130.298 SELECT * FROM words WHERE word REGEXP '^bre.*n$' ORDER BY word
This traced 5 queries, 4 of which took about 130 milliseconds.
A pgrep command was used to specify the PID of mysqld.
In this example, a lower threshold is used of 0.1 ms:
# ./mysqld_qslower.py `pgrep -n mysqld` 0.1
Tracing MySQL server queries for PID 14371 slower than 0.1 ms...
TIME(s) PID MS QUERY
0.000000 18608 24.201 SELECT COUNT(*) FROM words
13.242390 18608 130.378 SELECT * FROM words WHERE word REGEXP '^bre.*n$'
23.601751 18608 119.198 SELECT * FROM words WHERE word REGEXP '^zzzzzzzz$'
It worked, but I'm not catching any faster queries in this example. Notice I
added a query that searched for "zzzzzzzz": it returned an empty set, and ran
11 ms faster.
A 0 ms threshold can be specified to trace all queries:
# ./mysqld_qslower.py `pgrep -n mysqld` 0
Tracing MySQL server queries for PID 14371 slower than 0 ms...
TIME(s) PID MS QUERY
0.000000 18608 0.105 select @@version_comment limit 1
2.049312 18608 0.099 SELECT DATABASE()
2.050666 18608 0.274 show databases
2.051040 18608 0.176 show tables
5.730044 18608 130.365 SELECT count(*) AS count FROM words WHERE word REGEXP '^bre.*n$'
9.273837 18608 0.096 select 1
9.553742 18608 0.059 select 1
9.986087 18608 0.080 select 1
This includes an initialization of a mysql client command, and selecting the
database. I also added some "select 1;" queries, which do no work and return
quickly.
USAGE:
# ./mysqld_qslower.py -h
USAGE: mysqld_latency PID [min_ms]