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Re: Problems with pg_dump

From: Stefan Holzheu <stefan(dot)holzheu(at)bitoek(dot)uni-bayreuth(dot)de>
To: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: ADMIN <pgsql-admin(at)postgresql(dot)org>
Subject: Re: Problems with pg_dump
Date: 2004-01-26 19:29:33
Message-ID: 40156A9D.5040302@bitoek.uni-bayreuth.de (view raw or flat)
Thread:
Lists: pgsql-admin
> 
>>pg_dump: lost synchronization with server: got message type "5", length
>>842281016
> 
> 
>>The error does not occur always and not always with the same table. 
> 
> 
> Oh, that's even more interesting.  Is the failure message itself
> consistent --- that is, is it always complaining about "message type 5"
> and the same bizarre length value?  The "length" looks like it's really
> ASCII text ("2408" to be specific), so somehow libpq is misinterpreting
> a piece of the COPY datastream as the start of a new message.
> 

The failure looks similarly but the number do not exactly the same:

pg_dump: lost synchronization with server: got message type "4", length 
858863113
pg_dump: SQL command to dump the contents of table "aggr_max_hour" 
failed: PQendcopy() failed.
pg_dump: Error message from server: lost synchronization with server: 
got message type "4", length 858863113
pg_dump: The command was: COPY messungen.aggr_max_hour (id, von, wert, 
counts) TO stdout;

> 
>>However, the error occurs only on that kind of aggregation tables. There 
>>is a cron-job keeping the tables up to date, starting all 10 minutes. 
>>The job does delete and inserts on the table. Could this somehow block 
>>the dump process? Normally it should not?
> 
> 
> It's hard to see how another backend would have anything to do with
> this, unless perhaps the error is dependent on a particular data value
> that is sometimes present in the table and sometimes not.  It looks to
> me like either libpq or the backend is miscounting the number of data
> bytes in the COPY datastream.  Would it be possible for you to use a
> packet sniffer to capture the communication between pg_dump and the
> backend?  If we could look at exactly what's going over the wire, it
> would help to pin down the blame.
> 
Well, I never used a packet sniffer but if anyone tells me what to 
capture, I'd be glad to.

PostgreSQL is really a great piece of software, keep on making it even 
better!

Stefan



-- 
-----------------------------
Dr. Stefan Holzheu
Tel.: 0921/55-5720
Fax.: 0921/55-5799
BITOeK Wiss. Sekretariat
Universitaet Bayreuth
D-95440 Bayreuth
-----------------------------


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