Re: Some other things about contrib/bloom and generic_xlog.c

Teodor Sigaev <teodor(at)sigaev(dot)ru> writes:
>> 2. Unless I'm missing something, contrib/bloom is making no effort
>> to ensure that bloom index pages can be distinguished from other pages
>> by pg_filedump. That's fine if your expectation is that bloom will always
>> be a toy with no use in production; but otherwise, not so much. You need
>> to make sure that the last two bytes of the page special space contain a
>> uniquely identifiable code; compare spgist_page_id in SPGiST indexes.

> Now contrib/bloom is a canonical example how to implement yourown index and how
> to use generic WAL interface. And it is an useful toy: in some cases it could
> help in production system, patch attached. I'm a little dissatisfied with patch
> because I had to add unused field to BloomPageOpaqueData, in opposite case size
> of BloomPageOpaqueData struct equals 6 bytes but special size is MAXALIGNED, so,
> last two bytes will be unused. If unused field is not a problem, I will push
> this patch.

Yes, it will mean that the special space will have to be 8 bytes not 4.
But on the other hand, that only makes a difference on 32-bit machines;
if MAXALIGN is 8 then you won't be able to fit anything into those bytes
anyway. And someday there might be a use for the other two bytes ...
so I'm not particularly concerned by the "wasted space" argument.

regards, tom lane