bcc-dbstat man page

dbstat ā€” Collect histograms of MySQL/PostgreSQL query latencies.

Synopsis

dbstat [-v] [-p PID [PID ...]] [-m THRESHOLD] [-u] [-i INTERVAL] {mysql,postgres}

Description

This traces queries served by a MySQL or PostgreSQL server, and collects a histogram of query latencies. The histogram is printed at the end of collection, or at specified intervals.

This uses User Statically-Defined Tracing (USDT) probes, a feature added to MySQL and PostgreSQL for DTrace support, but which may not be enabled on a given installation. See requirements.

Since this uses BPF, only the root user can use this tool.

Requirements

CONFIG_BPF, bcc, and MySQL server with USDT probe support (when configuring the build: -DENABLE_DTRACE=1) or PostgreSQL server with USDT probe support (when configuring the build: --enable-dtrace).

Options

-h Print usage message.

-p PID

Trace this PID. If no PID is specified, the tool will attempt to automatically detect the MySQL or PostgreSQL processes running on the system.

-m THRESHOLD

Minimum query latency (duration) to trace, in milliseconds. Default is all queries.

-u

Display query latencies in microseconds (default: milliseconds).

-i INTERVAL

Print summaries (histograms) at this interval, specified in seconds.

{mysql,postgres}

The database engine to trace.

Examples

Display histogram of MySQL query latencies:

# dbstat mysql

Display histogram of PostgreSQL query latencies slower than 10ms in pid 408:

# dbstat postgres -p 408 -m 10

Display histogram of PostgreSQL query latencies at 3-second intervals:

# dbstat postgres -i 3

Overhead

This adds low-overhead instrumentation to queries, and only emits output data from kernel to user-level if they query exceeds the threshold. If the server query rate is less than 1,000/sec, the overhead is expected to be negligible. If the query rate is higher, test to gauge overhead.

Source

This is from bcc.

https://github.com/iovisor/bcc

Also look in the bcc distribution for a companion _examples.txt file containing example usage, output, and commentary for this tool.

OS

Linux

Stability

Unstable - in development.

Author

Sasha Goldshtein

See Also

dbslower(8)

Info

2017-02-15 USER COMMANDS