"Alex Turner" <armtuk(at)gmail(dot)com> writes:
> Home come the query statistics showed that 229066 blocks where read given
> that all the blocks in all the tables put together only total 122968?
You forgot to count the indexes. Also, the use of indexscans in the
mergejoins probably causes multiple re-reads of some table blocks,
depending on just what the physical ordering of the rows is.
regards, tom lane