Re: postgres under gdb

> Chris <chris(at)bitmead(dot)com> writes:
> > How do you run postgres under gdb?
>
> If you are running a standalone backend, you just fire it up.
> For normal use under a postmaster, the easiest thing I've found is to
> start psql (or your favorite client) in one window, start gdb on the
> postgres executable in another, and then "attach" to the already-started
> backend process. (Use "ps" to discover the backend's PID.) You must
> run gdb as postgres, of course, but the client process can belong to
> anyone.
>
> It gets a little tricky if you are trying to debug part of the
> backend startup sequence. We have a kluge for that: start psql
> with PGOPTIONS="-W n". That causes the backend to sleep() for n
> seconds fairly early in its startup, giving you time to attach to it
> before anything really interesting happens.
>
> In theory you can debug one backend in a live production system
> this way, but I wouldn't recommend doing that except in dire need.
> If you use gdb to stop the backend while it is holding a lock, you'll
> block other backends too --- and holding a spinlock is even worse,
> because those other backends will time out after a minute or so.
> Better to use a playpen installation.
>
> (Hey Bruce, shouldn't this info be in FAQ_DEV?)

I have added this to the main FAQ under debugging:

Another method is to start psql in one window, then find the PID of the
postgres process used by the psql. Use a debugger to attach to the
postgres PID. You can set breakpoints in the debugger and issue queries
from psql. If you are debugging postgres startup, you can set
PGOPTIONS="-W n", then start psql. This will cause startup to delay for
n seconds so you can attach with the debugger and trace through the
startup sequence.

--
Bruce Momjian | http://www.op.net/~candle
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