Database Reference
In-Depth Information
With automatic PGA memory management, so-called work areas are used for operations
such as sorts or hash joins. The target cumulative size of all active work areas is specified with
the parameter PGA_AGGREGATE_TARGET (PAT). A single process may access several work areas
concurrently. Information on automatic PGA memory management and work areas is avail-
able by querying dynamic performance views such as V$PGASTAT , V$PROCESS , V$SQL_WORKAREA ,
and V$SQL_WORKAREA_ACTIVE .
Misconceptions About PGA_AGGREGATE_TARGET
The parameter name PGA_AGGREGATE_TARGET is a name well chosen. What I'm trying to say is
that it is what it sounds like—a target, not an absolute limit, merely a target. This means that
the actual amount of memory consumed under high load may constantly, or at least intermit-
tently, be higher than the target value. But the implementation of automatic PGA memory
management is so well crafted that processes will then release memory, such that the total
memory consumption will soon drop below the target, if at all possible. Especially when PL/SQL,
which allocates a lot of memory, e.g., for collections such as index-by tables, is executed, the
target may be permanently exceeded. Whereas sort memory requirements can be reduced by
using temporary segments, PL/SQL memory requirements cannot.
Figure 1-2. PGA Sizing in Database Configuration Assistant
 
Search WWH ::




Custom Search