mirror of
https://github.com/postgres/postgres.git
synced 2025-04-27 22:56:53 +03:00
Add some documentation for DTrace support. Simon Riggs
This commit is contained in:
Tom Lane
parent
d92b939a0a
commit
606b10f959
@ -1,4 +1,4 @@
|
||||
<!-- $PostgreSQL: pgsql/doc/src/sgml/monitoring.sgml,v 1.39 2006/11/24 21:18:42 tgl Exp $ -->
|
||||
<!-- $PostgreSQL: pgsql/doc/src/sgml/monitoring.sgml,v 1.40 2006/12/02 00:42:54 tgl Exp $ -->
|
||||
|
||||
<chapter id="monitoring">
|
||||
<title>Monitoring Database Activity</title>
|
||||
@ -791,4 +791,281 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS procpid,
|
||||
<productname>PostgreSQL</productname>, refer to <xref linkend="mvcc">.
|
||||
</para>
|
||||
</sect1>
|
||||
|
||||
<sect1 id="dynamic-trace">
|
||||
<title>Dynamic Tracing</title>
|
||||
|
||||
<indexterm zone="dynamic-trace">
|
||||
<primary>DTrace</primary>
|
||||
</indexterm>
|
||||
|
||||
<para>
|
||||
<productname>PostgreSQL</productname> provides facilities to support
|
||||
dynamic tracing of the database server. This allows an external
|
||||
utility to be called at specific points in the code and thereby trace
|
||||
execution. Currently, this facility is primarily intended for use by
|
||||
database developers, as it requires substantial familiarity with the code.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
A number of trace points, often called probes, are already inserted
|
||||
into the source code. By default these probes are disabled, and
|
||||
the user needs to explicitly tell the configure script to make the
|
||||
probes available in <productname>PostgreSQL</productname>.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
Currently, only the DTrace utility is supported, which is only available
|
||||
on Solaris Express and Solaris 10+. It is expected that DTrace will
|
||||
be available in the future on FreeBSD and Mac OS X.
|
||||
Supporting other dynamic tracing utilities is theoretically possible by
|
||||
changing the definitions for the <literal>PG_TRACE</> macros in
|
||||
<filename>src/include/pg_trace.h</>.
|
||||
</para>
|
||||
|
||||
<sect2 id="compiling-for-trace">
|
||||
<title>Compiling for Dynamic Trace</title>
|
||||
|
||||
<para>
|
||||
By default, trace points are disabled, so you will need to
|
||||
explicitly tell the configure script to make the probes available
|
||||
in <productname>PostgreSQL</productname>. To include DTrace support
|
||||
in a 32-bit binary, specify <option>--enable-dtrace</> to configure.
|
||||
For example:
|
||||
<programlisting>
|
||||
$ ./configure --enable-dtrace ...
|
||||
</programlisting>
|
||||
To include DTrace support in a 64-bit binary, specify
|
||||
<option>--enable-dtrace</>
|
||||
and <literal>DTRACEFLAGS="-64"</> to configure. For example,
|
||||
using the gcc compiler:
|
||||
<programlisting>
|
||||
$ ./configure CC='gcc -m64' --enable-dtrace DTRACEFLAGS='-64' ...
|
||||
</programlisting>
|
||||
Using Sun's compiler:
|
||||
<programlisting>
|
||||
$ ./configure CC='/path_to_sun_compiler/cc -xtarget=native64' --enable-dtrace DTRACEFLAGS='-64' ...
|
||||
</programlisting>
|
||||
</para>
|
||||
</sect2>
|
||||
|
||||
<sect2 id="trace-points">
|
||||
<title>Built-in Trace Points</title>
|
||||
|
||||
<para>
|
||||
A few standard trace points are provided in the source code
|
||||
(of course, more can be added as needed for a particular problem).
|
||||
These are:
|
||||
</para>
|
||||
|
||||
<table id="trace-point-table">
|
||||
<title>Built-in Trace Points</title>
|
||||
<tgroup cols="3">
|
||||
<thead>
|
||||
<row>
|
||||
<entry>Name</entry>
|
||||
<entry>Parameters</entry>
|
||||
<entry>Overview</entry>
|
||||
</row>
|
||||
</thead>
|
||||
|
||||
<tbody>
|
||||
<row>
|
||||
<entry>transaction__start</entry>
|
||||
<entry>(int transactionId)</entry>
|
||||
<entry>The start of a new transaction.</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>transaction__commit</entry>
|
||||
<entry>(int transactionId)</entry>
|
||||
<entry>The successful completion of a transaction.</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>transaction__abort</entry>
|
||||
<entry>(int transactionId)</entry>
|
||||
<entry>The unsuccessful completion of a transaction.</entry>
|
||||
</row>
|
||||
|
||||
<row>
|
||||
<entry>lwlock__acquire</entry>
|
||||
<entry>(int lockid, int mode)</entry>
|
||||
<entry>An LWLock has been acquired.</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>lwlock__release</entry>
|
||||
<entry>(int lockid, int mode)</entry>
|
||||
<entry>An LWLock has been released.</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>lwlock__startwait</entry>
|
||||
<entry>(int lockid, int mode)</entry>
|
||||
<entry>An LWLock was not immediately available and a backend
|
||||
has begun to wait for the lock to become available.
|
||||
</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>lwlock__endwait</entry>
|
||||
<entry>(int lockid, int mode)</entry>
|
||||
<entry>A backend has been released from its wait for an LWLock.
|
||||
</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>lwlock__condacquire</entry>
|
||||
<entry>(int lockid, int mode)</entry>
|
||||
<entry>An LWLock was successfully acquired when the caller specified no
|
||||
waiting.
|
||||
</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>lwlock__condacquire__fail</entry>
|
||||
<entry>(int lockid, int mode)</entry>
|
||||
<entry>An LWLock was not successfully acquired when the caller specified
|
||||
no waiting.
|
||||
</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>lock__startwait</entry>
|
||||
<entry>(int locktag_field2, int lockmode)</entry>
|
||||
<entry>A request for a heavyweight lock (lmgr lock) has begun to wait
|
||||
because the lock is not available.
|
||||
</entry>
|
||||
</row>
|
||||
<row>
|
||||
<entry>lock__endwait</entry>
|
||||
<entry>(int locktag_field2, int lockmode)</entry>
|
||||
<entry>A request for a heavyweight lock (lmgr lock) has finished waiting
|
||||
(i.e., has acquired the lock).
|
||||
</entry>
|
||||
</row>
|
||||
</tbody>
|
||||
</tgroup>
|
||||
</table>
|
||||
</sect2>
|
||||
|
||||
<sect2 id="using-trace-points">
|
||||
<title>Using Trace Points</title>
|
||||
|
||||
<para>
|
||||
The example below shows a DTrace script for analyzing transaction
|
||||
counts on the system, as an alternative to snapshotting
|
||||
<structname>pg_stat_database</> before and after a performance test.
|
||||
<programlisting>
|
||||
#!/usr/sbin/dtrace -qs
|
||||
|
||||
postgresql$1:::transaction-start
|
||||
{
|
||||
@start["Start"] = count();
|
||||
self->ts = timestamp;
|
||||
}
|
||||
|
||||
postgresql$1:::transaction-abort
|
||||
{
|
||||
@abort["Abort"] = count();
|
||||
}
|
||||
|
||||
postgresql$1:::transaction-commit
|
||||
/self->ts/
|
||||
{
|
||||
@commit["Commit"] = count();
|
||||
@time["Total time (ns)"] = sum(timestamp - self->ts);
|
||||
self->ts=0;
|
||||
}
|
||||
</programlisting>
|
||||
Note how the double underline in trace point names needs to
|
||||
be replaced by a hyphen when using D script.
|
||||
When executed, the example D script gives output such as:
|
||||
<programlisting>
|
||||
# ./txn_count.d `pgrep -n postgres`
|
||||
^C
|
||||
|
||||
Start 71
|
||||
Commit 70
|
||||
Abort 1
|
||||
Total time (ns) 2312105013
|
||||
</programlisting>
|
||||
</para>
|
||||
<para>
|
||||
You should remember that trace programs need to be carefully written and
|
||||
debugged prior to their use, otherwise the trace information collected may
|
||||
be meaningless. In most cases where problems are found it is the
|
||||
instrumentation that is at fault, not the underlying system. When
|
||||
discussing information found using dynamic tracing, be sure to enclose
|
||||
the script used to allow that too to be checked and discussed.
|
||||
</para>
|
||||
</sect2>
|
||||
|
||||
<sect2 id="defining-trace-points">
|
||||
<title>Defining Trace Points</title>
|
||||
|
||||
<para>
|
||||
New trace points can be defined within the code wherever the developer
|
||||
desires, though this will require a re-compile.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
A trace point can be inserted by using one of the
|
||||
trace macros. These are chosen according to how many variables will
|
||||
be made available for inspection at that trace point. Tracing the
|
||||
occurrence of an event can be achieved with a single line, using
|
||||
just the trace point name, e.g.
|
||||
<programlisting>
|
||||
PG_TRACE (my__new__trace__point);
|
||||
</programlisting>
|
||||
More complex trace points can be provided with one or more variables
|
||||
for inspection by the dynamic tracing utility by using the
|
||||
<literal>PG_TRACE</><replaceable>n</> macro that corresponds to the number
|
||||
of parameters after the trace point name:
|
||||
<programlisting>
|
||||
PG_TRACE3 (my__complex__event, varX, varY, varZ);
|
||||
</programlisting>
|
||||
The definition of the transaction__start trace point is shown below:
|
||||
<programlisting>
|
||||
static void
|
||||
StartTransaction(void)
|
||||
{
|
||||
...
|
||||
|
||||
/*
|
||||
* generate a new transaction id
|
||||
*/
|
||||
s->transactionId = GetNewTransactionId(false);
|
||||
|
||||
XactLockTableInsert(s->transactionId);
|
||||
|
||||
PG_TRACE1(transaction__start, s->transactionId);
|
||||
|
||||
...
|
||||
}
|
||||
</programlisting>
|
||||
Note how the transaction ID is made available to the dynamic tracing
|
||||
utility.
|
||||
</para>
|
||||
|
||||
<para>
|
||||
The dynamic tracing utility may require you to further define these trace
|
||||
points. For example, DTrace requires you to add new probes to the file
|
||||
<filename>src/backend/utils/probes.d</> as shown here:
|
||||
<programlisting>
|
||||
provider postgresql {
|
||||
...
|
||||
probe transaction__start(int);
|
||||
...
|
||||
};
|
||||
</programlisting>
|
||||
</para>
|
||||
|
||||
<para>
|
||||
You should take care that the datatypes specified for the probe arguments
|
||||
match the datatypes of the variables used in the <literal>PG_TRACE</>
|
||||
macro. This is not checked at compile time. You can check that your newly
|
||||
added trace point is available by recompiling, then running the new binary,
|
||||
and as root, executing a DTrace command such as:
|
||||
<programlisting>
|
||||
dtrace -l -n transaction-start
|
||||
</programlisting>
|
||||
</para>
|
||||
</sect2>
|
||||
|
||||
</sect1>
|
||||
|
||||
</chapter>
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user