On 2014-09-27 12:11:16 -0400, Steve Singer wrote: > On 09/26/2014 06:05 PM, Andres Freund wrote: > >On 2014-09-26 14:57:12 -0400, Robert Haas wrote: > >Sure, it'll possibly not be trivial to move them elsewhere. On the other > >hand, the padding bytes have been unused for 8+ years without somebody > >laying "claim" on them but "me". I don't think it's a good idea to leave > >them there unused when nobody even has proposed another use for a long > >while. That'll just end up with them continuing to be unused. And > >there's actually four more consecutive bytes on 64bit systems that are > >unused. > > > >Should there really be a dire need after that, we can simply bump the > >record size. WAL volume wise it'd not be too bad to make the record a > >tiny bit bigger - the header is only a relatively small fraction of the > >entire content. > > If we were now increasing the WAL record size anyway for some unrelated > reason, would we be willing to increase it by a further 2 bytes for the node > identifier? > If the answer is 'no' then I don't think we can justify using the 2 padding > bytes just because they are there and have been unused for years. But if > the answer is yes, we feel this important enough to justfiy a slightly (2 > byte) larger WAL record header then we shouldn't use the excuse of maybe > needing those 2 bytes for something else. When something else comes along > that needs the WAL space we'll have to increase the record size.
I don't think that's a good way to see this. By that argument these bytes will never be used. Also there's four more free bytes on 64bit systems... > To say that if some other patch comes along that needs the space we'll redo > this feature to use the method Robert describes is unrealistic. If we think > that the replication identifier isn't general/important/necessary to > justify 2 bytes of WAL header space then we should start out with something > that doesn't use the WAL header, Maintaining complexity also has its costs. And I think that's much more concrete than some imaginary feature (of which nothing was heard for the last 8+ years) also needing two bytes. Greetings, Andres Freund -- Andres Freund http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
