Housekeeping article - mention BLOBs and their handles [DOC123]

[firebird-automations]

Submitted by: Arioch (arioch)

BLOBs are somewhat special case, they are kept outside the row and are handled somewhat differenlty.

More so, there is such a phenomenon as leaking BLOB IDs/handles by read-only read-committed never-ending transaction.
Such a transaction would not prevent regular table rows from being deleted->freed->collected but it may retain BLOBs for indefinite time.

http://www.firebirdsql.org/manual/gfix-housekeeping.html

I wish this article could make an *explicit* statement whether for that very context of GC and sweeping BLOBs are acting exactly like the rows referencing them or may have slightly different behavior in some situations.