I have a table with a bytea column which, of course, contains binary data. After 60 days, I no longer need the binary data but want to retain the rest of the record. Of course it's easy to just update the bytea column to null for the older records. But I can almost imagine this record on disk with a big "hole" in the middle where the bytea data used to be. Is there a PG daemon (the vacuum ?) that will "heal the hole" in time?
The freshly written record will not have a hole - either by virtue of variable width fields taking up basically their actual data space and also the fact that null is treated specially in the record format.
For the old row, yes you should read up on the how and why of the vacuum command.
