On fös, 2006-03-03 at 11:03 +0100, Paul Mackay wrote: > Hi, > > I've created a table like this : > CREATE TABLE tmp_A ( > c "char", > i int4 > ); > > And another one > CREATE TABLE tmp_B ( > i int4, > ii int4 > ); > > I then inserted a bit more than 19 million rows in each table (exactly > the same number of rows in each). > > The end result is that the physical size on disk used by table tmp_A > is exactly the same as table tmp_B (as revealed by the > pg_relation_size function) ! Given that a "char" field is supposed to > be 1 byte in size and a int4 4 bytes, shouldn't the tmp_A use a > smaller disk space ? Or is it that any value, whatever the type, > requires at least 4 bytes to be stored ? the int4 needs to be aligned at 4 bytes boundaries, making wasted space after the char. this would probably be the same size: CREATE TABLE tmp_C ( c "char", cc "char", i int4 ); and this would be smaller: CREATE TABLE tmp_D ( c "char", cc "char", ccc "char", ); P.S.: I did not actually check to see if the "char" type needs to be aligned, by I assumed not.
