## F.27. pg\_freespacemap

[F.27.1. Functions](pgfreespacemap.html#id-1.11.7.36.5)[F.27.2. Sample Output](pgfreespacemap.html#id-1.11.7.36.6)[F.27.3. Author](pgfreespacemap.html#id-1.11.7.36.7)

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 The `pg_freespacemap` module provides a means for examining the free space map (FSM). It provides a function called `pg_freespace`, or two overloaded functions, to be precise. The functions show the value recorded in the free space map for a given page, or for all pages in the relation.

 By default use is restricted to superusers and members of the `pg_stat_scan_tables` role. Access may be granted to others using `GRANT`.

### F.27.1. Functions

`pg_freespace(rel regclass IN, blkno bigint IN) returns int2` []()

 Returns the amount of free space on the page of the relation, specified by `blkno`, according to the FSM.

`pg_freespace(rel regclass IN, blkno OUT bigint, avail OUT int2)`

 Displays the amount of free space on each page of the relation, according to the FSM. A set of `(blkno bigint, avail int2)` tuples is returned, one tuple for each page in the relation.

 The values stored in the free space map are not exact. They're rounded to precision of 1/256th of `BLCKSZ` (32 bytes with default `BLCKSZ`), and they're not kept fully up-to-date as tuples are inserted and updated.

 For indexes, what is tracked is entirely-unused pages, rather than free space within pages. Therefore, the values are not meaningful, just whether a page is full or empty.

### F.27.2. Sample Output

```
postgres=# SELECT * FROM pg_freespace('foo');
 blkno | avail
### F.27.3. Author

 Original version by Mark Kirkwood `<[markir@paradise.net.nz](mailto:markir@paradise.net.nz)>`. Rewritten in version 8.4 to suit new FSM implementation by Heikki Linnakangas `<[heikki@enterprisedb.com](mailto:heikki@enterprisedb.com)>`

