Re: BUG #6602: concurrent psql session clobbers history

Peter Eisentraut <peter_e(at)gmx(dot)net> writes:
> On tor, 2012-04-19 at 15:00 -0400, Tom Lane wrote:
>> i+pgbugs(at)avdd(dot)tk writes:
>>> A concurrent psql session will overwrite the history of the first. This
>>> does not look good: a database tool causing me to lose my data!

>> Works okay for me. I suspect you need to take this up with whoever
>> packages libreadline for Ubuntu, because it's going to be libreadline's
>> problem not ours.

> It's probably actually using libedit for the history part.

[ after further research... ] Mmm, maybe. I can reproduce the
misbehavior on a Mac build using libedit. There is a relevant-looking
comment in psql's saveHistory function:

* On newer versions of libreadline, truncate the history file as
* needed and then append what we've added. This avoids overwriting
* history from other concurrent sessions (although there are still
* race conditions when two sessions exit at about the same time). If
* we don't have those functions, fall back to write_history().

A check of the configure output shows that Apple's libedit lacks
append_history(), so that the fallback code path is used. The phrasing
of this comment suggests that older versions of libreadline might be
lacking as well.

There's not a lot we can do about this issue when using a libreadline
or libedit that lacks the necessary support functions, I think.

regards, tom lane