there's no chance it can accidentally look like a valid segment. But when an existing segment is recycled, it gets a new header and that's it--the rest of the 16MB is still left behind from whatever was in that segment before. That means that even if you only write, say, 1MB of new
[...]
What clearxlogtail does is look inside the WAL segment, and it clears the "tail" behind the portion of that is really used. So our example file would end up with just the 1MB of useful data, followed by 15MB of
It sure would be nice if there was a way for PG itself to zero the unused portion of logs as they are completed, perhaps this will make it in as part of the ideas discussed on this list a while back to make a more "out of the box" log-ship mechanism?
I agree totally. I looked at the code for clearxlogtail and it seems short and not very complex. Hopefully something like this will at least be a trivial to set up option in 8.4.