Thanks Filip.I have 2 tables with 2 cols each( 1 numeric(8,0) and 1 varchar(3) ).In table1 both the cols are filled and in table2 the varchar colm is null So when I checked the tablesize for these two tables (using pg_relation_size)table1 - 57344 bytes (no null columns)table2 - 49152 bytes (varchar colm is null) There is not much difference between the two sizes.So even if a columnis null postgresql still has lots of overhead. Does postgres occupy space even when the column is NULL? This is not a spam.... I posted it twice becoz my question didnotshow up the first time in the mailing list even after 30 minutes. So itried again and then both showed up...kind of strange though! Thanks againJosh On Nov 19, 2007 1:37 PM, Filip Rembiałkowski <plk.zuber@xxxxxxxxx> wrote:> 2007/11/19, Josh Harrison <joshques@xxxxxxxxx>:> > Hi,> > I have a few questions about the storage and performance> >> > 1. How do you estimate the table size in postgresql?> > For example if I have a table 'Dummy' with 1 varchar (40) & 1> > numeric(22,0) fields and 1000 rows, what is the tablesize estimate for> > this (including the row overhead etc)? How many pages will this> > occupy?> >> > 2. Also if the table contains null columns, does postgres allocates> > the same space for these nulls columns? How does it handle 'nulls' in> > terms of storage?>> Try these:> http://www.postgresql.org/docs/current/static/datatype-numeric.html> http://www.postgresql.org/docs/current/static/datatype-character.html> http://www.postgresql.org/docs/current/static/storage-page-layout.html>> ad.1 ) There is a fixed-size header (occupying 27 bytes on most> machines) for each tuple>> so you will have about 27 + 1 + varchar data + numeric data per row,> plus some overhaed for block headers>> ad.2 ) there is a null bitmap for each tuple which has nullable fields> - so every 8 NULLable columns occupy one byte bitmap.>>> PS. why do you post same thing many times? this is kinda.. spam?>> --> Filip Rembiałkowski> ---------------------------(end of broadcast)---------------------------TIP 6: explain analyze is your friend
