Re: Compression of full-page-writes

On Fri, Dec 12, 2014 at 10:23 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Thu, Dec 11, 2014 at 10:33 PM, Michael Paquier
> <michael.paquier@gmail.com> wrote:
>> On Tue, Dec 9, 2014 at 4:09 AM, Robert Haas <robertmhaas@gmail.com> wrote:
>>> On Sun, Dec 7, 2014 at 9:30 PM, Simon Riggs <simon@2ndquadrant.com> wrote:
>>> > * parameter should be SUSET - it doesn't *need* to be set only at
>>> > server start since all records are independent of each other
>>>
>>> Why not USERSET?  There's no point in trying to prohibit users from
>>> doing things that will cause bad performance because they can do that
>>> anyway.
>>
>> Using SUSET or USERSET has a small memory cost: we should
>> unconditionally palloc the buffers containing the compressed data
>> until WAL is written out. We could always call an equivalent of
>> InitXLogInsert when this parameter is updated but that would be
>> bug-prone IMO and it does not plead in favor of code simplicity.
>
> I don't understand what you're saying here.
I just meant that the scratch buffers used to store temporarily the
compressed and uncompressed data should be palloc'd all the time, even
if the switch is off.
-- 
Michael