Thread: Durability?

Hi,

I got an error like this:

ERROR:  xlog flush request 1/C121E998 is not satisfied --- flushed only to 1/BCBCB440
CONTEXT:  writing block 529 of relation 1663/233690/1247
WARNING:  could not write block 529 of 1663/233690/1247
DETAIL:  Multiple failures --- write error might be permanent.

The xrecoff value (logs show 1/xrecoff) advances a few times during the day, but the message keeps appearing.

I am not sure to understand clearly the consequences of such error since Postgres continues to accept new transactions.
Ifmy WAL is corrupted, are my transactions still durable?
 
If this is a violation of durability, is there a way to force Postgres to terminate on such error?

Thanks in advance for the clarification.
Emmanuel

Emmanuel Cecchet <manu@frogthinker.org> writes:
> I got an error like this:

> ERROR:  xlog flush request 1/C121E998 is not satisfied --- flushed only to 1/BCBCB440
> CONTEXT:  writing block 529 of relation 1663/233690/1247
> WARNING:  could not write block 529 of 1663/233690/1247
> DETAIL:  Multiple failures --- write error might be permanent.

> The xrecoff value (logs show 1/xrecoff) advances a few times during the day, but the message keeps appearing.

It looks like you've got a corrupted page in shared buffers, and every
time the system tries to flush it to disk for a checkpoint, it fails.

What I'd try for getting out this is to kill -9 some backend in order
to force a database restart.  Of course, if you want to investigate
what caused it, you should dig around in shared memory first and try
to get a copy of that buffer's contents.
        regards, tom lane

Tom Lane wrote:
> Emmanuel Cecchet <manu@frogthinker.org> writes:
>   
>> I got an error like this:
>>     
>
>   
>> ERROR:  xlog flush request 1/C121E998 is not satisfied --- flushed only to 1/BCBCB440
>> CONTEXT:  writing block 529 of relation 1663/233690/1247
>> WARNING:  could not write block 529 of 1663/233690/1247
>> DETAIL:  Multiple failures --- write error might be permanent.
>>     
>
>   
>> The xrecoff value (logs show 1/xrecoff) advances a few times during the day, but the message keeps appearing.
>>     
>
> It looks like you've got a corrupted page in shared buffers, and every
> time the system tries to flush it to disk for a checkpoint, it fails.
>
> What I'd try for getting out this is to kill -9 some backend in order
> to force a database restart.  Of course, if you want to investigate
> what caused it, you should dig around in shared memory first and try
> to get a copy of that buffer's contents.
>   
Will the database be able to restart with a corrupted WAL?
If the database restarts, what transactions will be missing:
- just the block that couldn't be flushed?
- all transactions that were committed after the faulty block?
- more?

Thanks
Emmanuel

Emmanuel Cecchet <manu@frogthinker.org> writes:
> Tom Lane wrote:
>> It looks like you've got a corrupted page in shared buffers, and every
>> time the system tries to flush it to disk for a checkpoint, it fails.

> Will the database be able to restart with a corrupted WAL?

I don't think you have a corrupted WAL.
        regards, tom lane