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

On Wed, Mar 31, 2010 at 12:54 AM, Fujii Masao <masao(dot)fujii(at)gmail(dot)com> wrote:
> On Wed, Mar 31, 2010 at 12:06 PM, Robert Haas <robertmhaas(at)gmail(dot)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

Well, that might still leave someone confused if they had one standby
and were trying to bring up a second one.

...Robert