Re: sorry, too many standbys already vs. MaxWalSenders vs. max_wal_senders

On Wed, Mar 31, 2010 at 12:06 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> After snapshotting my master using hot backup to create a workable
> slave instance, I created recovery.conf on the slave and tried to get
> it to connect to the master and stream WAL.
>
> This led to the message "sorry, too many standbys already", which did
> not immediately clue me in as to what I needed to do to fix the
> problem.  Grepping the source code for the error message revealed that
> the problem was that MaxWalSenders was zero.  A few seconds further
> head-scratching revealed that this was the GUC max_wal_senders, which
> I duly increased from 0 to 1, after which it worked.
>
> I think perhaps this error message needs some adjustment.  It should
> be reasonably possible to guess the name of the GUC that needs
> increasing based on the error message, and it currently isn't.

Agreed. How about the atteched patch?
The patch treats differently the case where max_wal_senders is 0,
and the following error message (better message?) is written only
in this case.

    could not accept connection from the standby because max_wal_senders is 0

Regards,

--
Fujii Masao
NIPPON TELEGRAPH AND TELEPHONE CORPORATION
NTT Open Source Software Center