Re: literature on write-ahead logging

On Thu, Jun 9, 2011 at 10:22 AM, Alvaro Herrera
<alvherre@commandprompt.com> wrote:
>> 1. Subdivide XLOG insertion into three operations: (1) allocate space
>> in the log buffer, (2) copy the log records into the allocated space,
>> and (3) release the space to the buffer manager for eventual write to
>> disk.  AIUI, WALInsertLock currently covers all three phases of this
>> operation, but phase 2 can proceed in parallel.  It's pretty easy to
>> imagine maintain one pointer that references the next available byte
>> of log space (let's call this the "next insert" pointer), and a second
>> pointer that references the byte following the last byte known to be
>> written (let's call this the "insert done" pointer).
>
> I think this can be done more simply if instead of a single "insert
> done" pointer you have an array of them, one per backend; there's also a
> global pointer that can be advanced per the minimum of the bunch, which
> you can calculate with some quick locking of the array.  You don't need
> to sleep at all, except to update the array and calculate the global
> ptr, so this is probably also faster.

I think looping over an array with one entry per backend is going to
be intolerably slow...  but it's possible I'm wrong.

--
Robert Haas
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