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Demonstrations of dbstat, the Linux eBPF/bcc version.
dbstat traces queries performed by a MySQL or PostgreSQL database process, and
displays a histogram of query latencies. For example:
# dbstat mysql
Tracing database queries for pids 25776 slower than 0 ms...
query latency (ms) : count distribution
0 -> 1 : 990 |****************************************|
2 -> 3 : 7 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 0 | |
1024 -> 2047 : 2 | |
^C
It's immediately evident that the vast majority of queries finish very quickly,
in under 1ms, but there are some super-slow queries occasionally, in the 1-2
seconds bucket.
We can filter out the shorter queries with the -m switch:
# dbstat mysql -m 1000
Tracing database queries for pids 25776 slower than 1000 ms...
query latency (ms) : count distribution
0 -> 1 : 0 | |
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 0 | |
1024 -> 2047 : 8 |****************************************|
^C
By default, dbstat will try to detect mysqld and postgres processes, but if
necessary, you can specify the process ids with the -p switch. Here, the -i
switch is also used to request histograms at 3 second intervals:
# dbstat mysql -p $(pidof mysql) -i 3
Tracing database queries for pids 25776 slower than 0 ms...
[06:14:36]
query latency (ms) : count distribution
0 -> 1 : 758 |****************************************|
2 -> 3 : 1 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 0 | |
1024 -> 2047 : 1 | |
[06:14:39]
query latency (ms) : count distribution
0 -> 1 : 436 |****************************************|
2 -> 3 : 2 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 0 | |
1024 -> 2047 : 1 | |
[06:14:42]
query latency (ms) : count distribution
0 -> 1 : 399 |****************************************|
2 -> 3 : 0 | |
4 -> 7 : 0 | |
8 -> 15 : 0 | |
16 -> 31 : 0 | |
32 -> 63 : 0 | |
64 -> 127 : 0 | |
128 -> 255 : 0 | |
256 -> 511 : 0 | |
512 -> 1023 : 0 | |
1024 -> 2047 : 1 | |
^C
USAGE:
# dbstat -h
usage: dbstat.py [-h] [-v] [-p [PID [PID ...]]] [-m THRESHOLD] [-u]
[-i INTERVAL]
{mysql,postgres}
positional arguments:
{mysql,postgres} the database engine to use
optional arguments:
-h, --help show this help message and exit
-v, --verbose print the BPF program
-p [PID [PID ...]], --pid [PID [PID ...]]
the pid(s) to trace
-m THRESHOLD, --threshold THRESHOLD
trace queries slower than this threshold (ms)
-u, --microseconds display query latencies in microseconds (default:
milliseconds)
-i INTERVAL, --interval INTERVAL
print summary at this interval (seconds)
dbstat postgres # display a histogram of PostgreSQL query latencies
dbstat mysql -v # display MySQL latencies and print the BPF program
dbstat mysql -u # display query latencies in microseconds (default: ms)
dbstat mysql -m 5 # trace only queries slower than 5ms
dbstat mysql -p 408 # trace queries in a specific process
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