Thanks for all the responses.... On 5 February 2013 19:36, Rosser Schwarz <rosser.schw...@gmail.com> wrote: > > On Tue, Feb 5, 2013 at 11:00 AM, Scott Mead <sco...@openscg.com> wrote: >> >> Agreed, don't forget, you have indexes, free space, vacuum-able stuff, >> etc... all laying in your datafiles. Your measurements are telling you >> what you have purely in a raw form. >> > Indexes are stored separately. There should be no free space (why would there be? FILLFACTOR is 100!) and I've vacuumed already.
Additionally, postgres has a number of "metadata" columns (e.g., xmin, > xmax, cmin, cmax, &c). Those can add up, particularly when their net size > is greater than the user data size of a row. > That's a fair point. 611MB (actual disk size) - 138MB (summed data size) = 483MB 11M rows (ish). That's nearly 48 bytes extra per row. http://www.postgresql.org/docs/9.2/static/storage-page-layout.html gives detail... Let's say around 249MB (23 bytes per row, according to that page) for the columns you mention, so that leaves 234MB unexplained. I can see 44 bytes per page header (given 5 columns, so 20 bytes ItemIdData, with 24 bytes PageHeaderData). Given page size of 8kb that would imply page headers of about 3.3MB over a 611MB table. Even with some bytes for alignment I'm Still not seeing where 230MB (more than the space taken by the data itself) of my disk is gone. Thanks! Geoff
