Re: Slony uninstall info/warning

Thanks for the info, Richard.

I didn't think that it was a slony issue per se, but that a note should
be added to the slony docs warning to recycle connections after making
substantive changes to the schema.

You're right, we use both (java) prepared statements and pl/pgsql functions.

The data loss aspect is not so clear cut (for us). We definitely got
records that failed to insert (missing sequence numbers in tables) while
others did insert correctly into the same tables (using the same
pl/pgsql functions). So we can't figure out what the pattern is.

Although we do have our connection pool recycle idle connections - it
could be that things worked when a new recycled connection was used by
the web app, and failed when one of the "old/original" connections was
used. This is probably what masked the errors for us...

It would be great if postgres could "recompile" pl/pgsql functions
whenever it found a missing object referenced within the function -
chances are that it would compile cleanly (in this case) and then could
be executed without error.

something along the lines of

execute function
OK -> return result
ERROR - OID -> recompile function, and re-execute
   OK -> return result
   ERROR - OID -> report error

This would help get rid of the temp table in functions work around
having to use an execute statement.

Thanks for your help and feedback.

John Sidney-Woollett

Richard Huxton wrote:

> John Sidney-Woollett wrote:
>
>> Hopefully this will prevent data loss or problems for others using
>> slony 1.0.5 and pg 7.4.6...
>>
>> We just got bitten by something we didn't foresee when completely
>> uninstalling a slony replication cluster from the master and slave...
>>
>> MAKE SURE YOU STOP YOUR APPLICATION RUNNING AGAINST YOUR MASTER
>> DATABASE WHEN REMOVING THE WHOLE SLONY CLUSTER, or at least re-cycle
>> all your open connections after the event!
>>
>> The connections appear to "remember" or refer to objects which are
>> removed by the uninstall node script. And you get lots of errors as a
>> result (and possible data loss??)...
>>
>> Question: Why do our database objects still refer to removed slony
>> objects after they are removed?
>
>
> Well, there are two areas I know cache plans/OIDs:
>  1. Prepared statements
>  2. plpgsql functions
>
> At a guess, since you mention Java the first almost certainly applies to
> you.
>
> This isn't a slony issue so much as a cached plan issue. I'm guessing
> the same problems would occur if you were manually changing the database
> schema.
>
> Don't think you could get data loss (unless the application ignores
> errors). You will however get to see a wide range of OID related errors.
>
> --
>   Richard Huxton
>   Archonet Ltd