On Thu, Nov 1, 2018 at 2:29 PM Stephen Frost <sfr...@snowman.net> wrote:
> Greetings, > > * Paul Ramsey (pram...@cleverelephant.ca) wrote: > > The attached patch adds in a code path to do a partial decompression of > the > > TOAST entry, when the requested slice is at the start of the object. > > There two things that I wonder about in the patch- if it would be of any > use to try and allocate on a need basis instead of just allocating the > whole chunk up to the toast size, I'm not sure what I was thinking when I rejected allocating the slice size in favour of the whole uncompressed size... I cannot see why that wouldn't work. > and secondly, why we wouldn't consider > handling a non-zero offset. A non-zero offset would, of course, still > require decompressing from the start and then just throwing away what we > skip over, but we're going to be doing that anyway, aren't we? Why not > stop when we get to the end, at least, and save ourselves the trouble of > decompressing the rest and then throwing it away. > I was worried about changing the pg_lz code too much because it scared me, but debugging some stuff made me read it more closely so I fear it less now, and doing interior slices seems not unreasonable, so I will give it a try. P
