Tom Lane wrote:
Tatsuo Ishii wrote:

BTW, I noticed difference of outputs from pg_freespacemap and

I ran pgbench and inspected "accounts" table by using these tools.

sum of bytes: 250712

free_space: 354880

Shouldn't they be identical?

vacuum/fsm disregard pages with "uselessly small" amounts of
free space (less than the average tuple size, IIRC).

Ah - that what I was seeing! Thanks.

I do notice a rather serious shortcoming of pg_freespacemap in its
current incarnation, which is that it *only* shows you the per-page free
space data, and not any of the information that would let you determine
what the FSM is doing to filter the raw data.  The per-relation
avgRequest and lastPageCount fields would be interesting for instance.
Perhaps there should be a second view with one row per relation to
carry the appropriate data.

Ok - I did wonder about 2 views, but was unsure if the per-relation stuff was interesting. Given that it looks like it is interesting, I'll see about getting a second view going.



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