Re: shared_buffers, wal_buffers, WAL files, data files

Alvaro Herrera a écrit :
> Guillaume Lelarge wrote:
>> Tom Lane a écrit :
>>> Guillaume Lelarge <guillaume@lelarge.info> writes:
>>>> I try to answer a simple question : what happens when I do a simple
>>>> "INSERT" on a just started PostgreSQL server.
>>>> From what I understand with the INSERT statement, here is what happens :
>>>>  * backend loads first (and only) block from footable file into a shared
>>>>    buffer
>>>>  * it modifies this block on the shared buffer, and sets it as dirty
>>> Right, and it also makes a WAL log entry about this action.
>>>
>> The WAL log entry is made on the wal buffers (in memory). As soon as
>> this statement is commited (in my example, it's right now, but in a
>> BEGIN ... COMMIT statement, at COMMIT time), the wal buffer is flushed
>> on WAL files. It can be flushed before if wal buffer is not big enough
>> to contain all the current transactions. Am I right ?
> 
> That's correct.  WAL buffers are obviously shared; when one transaction
> commits it will flush not only its own entries, but also those that any
> other transaction could have written.
> 

OK, thanks. I'll probably have more questions but I need to think a bit
more about all your answers.

Anyways, thanks.

Regards.


-- 
Guillaume.http://www.postgresqlfr.orghttp://dalibo.com