Re: [HACKERS] increasing the default WAL segment size

On 3/17/17 16:20, Peter Eisentraut wrote:
> On 3/16/17 21:10, Robert Haas wrote:
>> The changes to pg_standby seem to completely break the logic to wait
>> until the file has attained the correct size.  I don't know how to
>> salvage that logic off-hand, but just breaking it isn't acceptable.
> 
> I think we would have to extend restore_command with an additional
> placeholder that communicates the segment size, and add a new pg_standby
> option to accept that size somehow.  And specifying the size would have
> to be mandatory, for complete robustness.  Urgh.

Another way would be to name the WAL files in a more self-describing
way.  For example, instead of

000000010000000000000001
000000010000000000000002
000000010000000000000003

name them (for 16 MB)

000000010000000001
000000010000000002
000000010000000003

Then, pg_standby and similar tools can compute the expected file size
from the file name length: 16 ^ (24 - fnamelen)

However, that way you can't actually support 64 MB segments.  The next
jump up would have to be 256 MB (unless you want to go to a base other
than 16).

-- 
Peter Eisentraut              http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services