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