Re: How to recover from compressed wal archieve in windows

On 5/20/20 6:27 PM, Michael Paquier wrote:
> On Wed, May 20, 2020 at 11:36:09AM -0700, Adrian Klaver wrote:
>> The next problem is that I'm pretty sure a WAL file with *.gz extension will
>> not be able to be processed directly by the server. So you are going to have
>> to uncompress it at some point before it gets restored.
> 
> The short answer to that question is no.  The backend does not
> uncompress the segment file.  What happens is that the restore command
> copies the file defined by %f to the location of %p where is gets
> renamed to RECOVERYXLOG, and we expect the restore command to drop a
> 16MB file in og_wal/.  There is a check on the size, which would fail
> if the WAL segment is still compressed.  This logic is in
> RestoreArchivedFile() in xlogarchive.c.

I figured that would be the case.

So how is this handled?:

wal_compression (boolean)

     When this parameter is on, the PostgreSQL server compresses a full 
page image written to WAL when full_page_writes is on or during a base 
backup. A compressed page image will be decompressed during WAL replay. 
The default value is off. Only superusers can change this setting.


> --
> Michael
> 


-- 
Adrian Klaver
adrian.klaver@aklaver.com