Ühel kenal päeval, E, 2007-02-12 kell 17:23, kirjutas Heikki Linnakangas: > [EMAIL PROTECTED] wrote: > > On Mon, Feb 12, 2007 at 12:48:06AM -0500, Tom Lane wrote: > >> We just finished sweating blood to get the tuple header size down to 23 > >> bytes from 27 (which saves 8 bytes not 4 if MAXALIGN=8). We are not > >> going to blow that again on HOT. > > > > I haven't had enough time to follow all of the details here - but if the > > ability to update a row with minimal overhead, as long as there is extra > > room in the same block is a great idea (it sounds appealing to me) - could > > it be done with just a 1 byte list? 24 instead of 23 for the tuple size. > > Assuming 8k pages, you could in theory store reference to a line pointer > in just 1 byte. > > But actually that 1 free byte in the header is not currently just waste > of space. If you have any nulls in your tuple, there's going to be a > null bitmap in addition to the header. 1 byte is conveniently enough to > store the null bitmap for a table with max 8 columns,
Are we actually doing that ? I.E are null bitmaps really allocated in 1 byte steps nowadays ? > and if a table has > more than 8 columns, the extra 4 or 8 bytes needed for the null bitmap > probably doesn't matter so much because the tuples are quite wide anyway. > -- ---------------- Hannu Krosing Database Architect Skype Technologies OÜ Akadeemia tee 21 F, Tallinn, 12618, Estonia Skype me: callto:hkrosing Get Skype for free: http://www.skype.com ---------------------------(end of broadcast)--------------------------- TIP 7: You can help support the PostgreSQL project by donating at http://www.postgresql.org/about/donate