On Fri, Apr 19, 2013 at 10:17 AM, Will Childs-Klein <willc...@gmail.com> wrote: > Hello All, > I'm writing today to inquire about finding the exact point in the source > where postgres writes to disk. I'm trying to implement some compression in > postgres. The idea is to compress the data right when its written to disk, > to reduce the amount of data written to disk, reducing the amount of time of > disk read/write. I'm hoping that this reduction in disk IO latency is > greater than the CPU cost incurred by compression, resulting in a speedup. I > will be testing various compression libraries to see which (if any) work > well for various query types. I've been looking through the source code, in > src/backend/storage specifically. I'm thinking something in smgr is where i > want to make my de/compress calls. Specifically in > src/backend/storage/smgr/md.c in the functions mdwrite(...) and mdread(...). > Am I in the right place? If not where should I look?
this is not going to work. postgres tables are page organized -- if you compress pages as they are written out they become variable length. this in turn would cause the entire file to have to shift up if you wrote a page back and the size grew. as noted, postgres already compresses the most interesting case -- when a single tuple spans pages (aka toast). merlin -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
