Re: Losing records when server hang

Scott Marlowe wrote:

>On Mon, 2004-08-09 at 09:07, lec wrote:
>
>
>>Scott Marlowe wrote:
>>
>>
>>>On Sun, 2004-08-08 at 21:26, Alvaro Herrera Munoz wrote:
>>>
>>>
>>>
>>>>On Sun, Aug 08, 2004 at 08:36:36PM -0600, Scott Marlowe wrote:
>>>>
>>>>
>>>>
>>>>>On Sun, 2004-08-08 at 19:43, lec wrote:
>>>>>
>>>>>
>>>>>
>>>>>>If I commit the following records 1,2,3,4,5,6,7,8,9,10 to the database
>>>>>>and the server hangs, I could lose records 5,6,7,8,9 but record 10 is
>>>>>>there. How is this possible and do anyone know how Postgresql
>>>>>>physically writes the records?
>>>>>>
>>>>>>
>>>>>>
>>>>>Assuming a properly function storage subsystem and a kernel that does
>>>>>not lie about fsync, this is not possible.
>>>>>
>>>>>
>>>>>
>>I'm using Redhat 7.3, kernel 2.4.18
>>
>>
>>>>It is actually possible if he uses several backends to do the job, and
>>>>transaction inserting record 10 commits before the hang, and 5,6,7,8,9
>>>>don't.
>>>>
>>>>
>>>>
>>Just 1 backend.
>>
>>
>>>Yeah, but he explicitly said he'd committed 1 through 10. Unless he
>>>didn't understand what is meant by commit. I.e. committing AND
>>>receiving the ack for that commit. Until the database says it
>>>committed, nothing's been committed, so he might have thought just
>>>firing the insert query was committing. I hadn't really thought of that
>>>angle.
>>>
>>>Is that the case, lec?
>>>
>>>
>>>
>>I explicitly 'COMMIT'
>>
>>
>>>
>>>
>>>
>>>>If this is only one backend, then I'd love to see how did he do that.
>>>>
>>>>
>>>>
>>>Me too :-)
>>>
>>>
>>>
>>>
>>>
>>That's exactly leaving me puzzled. I don't know if it has anything to
>>do with the SCSI controller or hardware related stuff. The controller
>>is a RAID, configured are RAID-5.
>>
>>
>
>Does that RAID controller have NON battery backed cache?
>
>
>
>
I'm not sure.