Re: 9.3 Beta1 status report

On 22.04.2013 23:06, Bruce Momjian wrote:
> On Mon, Apr 22, 2013 at 10:11:48PM +0300, Heikki Linnakangas wrote:
>>> E.1.3.2.1. Write-Ahead Log (WAL)
>>>
>>> Store WAL in a continuous stream, rather than skipping the last 16MB segment every 4GB (Heikki Linnakangas) BACKWARD COMPATIBLE BREAK
>>>
>>> Restructure WAL files to better handle timeline changes during recovery (Heikki Linnakangas)
>>>
>>> Restructure WAL files to use a more compact storage format (Heikki Linnakangas)
>>
>> Can you clarify which commits these came from? The first one is
>> clear (dfda6eba), and I think the 3rd covers commits 20ba5ca6 and
>> 061e7efb1. But what is that second entry?
>
> Frankly, I found the WAL and timeline commits all over the place and
> could hardly make sense of it. I tried to collapse entries into
> meaningful items, but I need help. Can you suggest changes?

Ok:

* Don't skip the last 16 MB WAL segment every 4GB, with filename ending
in FF (Heikki Linnakangas) BACKWARD COMPATIBLE BREAK

* Change WAL record format, allowing the record header to be split
across pages. The new format is slightly more compact. (Heikki Linnakangas)

In "Source Code" section:

* Use a 64-bit integer to represent WAL positions (XLogRecPtr), instead
of two 32-bit integers. (Heikki Linnakangas)

Do we usually repeat the changes listed in the backwards compatibility
section later, in the "Changes" section? If not, then instead of the
first two items above, let's just have these in the
backwards-compatibility section:

* The WAL file numbering has changed to not skip WAL files ending with FF.

If you have e.g backup / restore scripts that took the skipping into
account, they need to be adjusted.

* The WAL format has changed.

Any external tools that read the WAL files need to be adjusted to
understand the new format. The new xlogreader facility helps
writing such tools.

- Heikki