Re: Write Ahead Logging for Hash Indexes

Stephen Frost <sfrost(at)snowman(dot)net> writes:
> * Tom Lane (tgl(at)sss(dot)pgh(dot)pa(dot)us) wrote:
>> It's true that as soon as we need another overflow page, that's going to
>> get dropped beyond the 2^{N+1}-1 point, and the *apparent* size of the
>> index will grow quite a lot. But any modern filesystem should handle
>> that without much difficulty by treating the index as a sparse file.

> Uh, last I heard we didn't allow or want sparse files in the backend
> because then we have to handle a possible out-of-disk-space failure on
> every write.

For a hash index, this would happen during a bucket split, which would
need to be resilient against out-of-disk-space anyway.

>> There may be some work to be done in places like pg_basebackup to
>> recognize and deal with sparse files, but it doesn't seem like a
>> reason to panic.

> Well, and every file-based backup tool out there..

Weren't you the one leading the charge to deprecate use of file-based
backup?

regards, tom lane