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 column is 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 didnot show up the first time in the mailing list even after 30 minutes. So i tried again and then both showed up...kind of strange though! Thanks again Josh On Nov 19, 2007 1:37 PM, Filip Rembiałkowski <[EMAIL PROTECTED]> wrote: > 2007/11/19, Josh Harrison <[EMAIL PROTECTED]>: > > 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