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Enter automatic PGA memory management. Here, you first simply set up and size the SGA. The SGA is a fixed-size piece of memory so you can very accurately see how big it is, and that will be its total size (unless and until you change it). You then tell Oracle, "This is how much memory you should try to limit yourself to across all work areas (a new umbrella term for the sorting and hashing areas you use). Now, you could in theory take a machine with 2GB of physical memory and allocate 768MB of memory to the SGA and 768MB of memory to the PGA, leaving 512MB of memory for the OS and other processes. I say "in theory" because it doesn't work exactly that cleanly, but it's close. Before I discuss why that s true, let s take a look at how to set up automatic PGA memory management and turn it on. The process of setting this up involves deciding on the proper values for two instance initialization parameters: WORKAREA_SIZE_POLICY: This parameter may be set to either MANUAL, which will use the sort area and hash area size parameters to control the amount of memory allocated, or AUTO, in which case the amount of memory allocated will vary based on the current workload in the database. The default and recommended value is AUTO. PGA_AGGREGATE_TARGET: This parameter controls how much memory the instance should allocate, in total, for all work areas used to sort or hash data. Its default value varies by version and may be set by various tools such as the DBCA. In general, if you are using automatic PGA memory management, you should explicitly set this parameter.

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Note In Oracle 11g Release 1 and above, instead of setting the PGA_AGGREGATE_TARGET, you can set the

The types inferred for the code in Listing 13-2 are as follows: type IterativeBackgroundWorker<'state> = new : ('state -> 'state) * 'state * int -> IterativeBackgroundWorker<'state> member RunWorkerAsync : unit -> unit member CancelAsync : unit -> unit member member member member ProgressChanged WorkerCompleted WorkerCancelled WorkerError : : : : IEvent<int * 'state> IEvent<'state> IEvent<unit> IEvent<exn>

MEMORY_TARGET parameter. When the database uses the MEMORY_TARGET parameter, it decides how much memory

to allocate to the SGA and PGA respectively. It may also decide to reallocate these memory amounts while the database is up and running. This fact, however, doesn t affect how automatic PGA memory management (described below) works; rather it just decides the setting for the PGA_AGGREGATE_TARGET.

Let s take a look at this signature first, because it represents the design of the type. The worker constructor is given a function of type 'state -> 'state to compute successive iterations of the computation, plus an initial state and the number of iterations to compute. For example, you can compute the Fibonacci numbers using the following iteration function: let fibOneStep (fibPrevPrev:bigint,fibPrev) = (fibPrev, fibPrevPrev+fibPrev);; The type of this function is as follows:

So, assuming that WORKAREA_SIZE_POLICY is set to AUTO and PGA_AGGREGATE_TARGET has a nonzero value, you will be using the new (as of Oracle 9i) automatic PGA memory management. You can turn it on in your session via the ALTER SESSION command or at the system level via the ALTER SYSTEM command.

Note Bear in mind the previous caveat that in Oracle9i, shared server connections will not use automatic

The RunWorkerAsync and CancelAsync members follow the BackgroundWorker design pattern, as do the events, except that we have expanded the RunWorkerCompleted event into three events to correspond to the three termination conditions and modified the ProgressChanged to include the state. You can instantiate the type as follows: > let worker = new IterativeBackgroundWorker<_>( fibOneStep,(1I,1I),100);; val worker : IterativeBackgroundWorker<bigint * bigint> > worker.WorkerCompleted.Add(fun result -> MessageBox.Show(sprintf "Result = %A" result) |> ignore);; val it : unit = () > worker.ProgressChanged.Add(fun (percentage, state) -> printfn "%d%% complete, state = %A" percentage state);; val it : unit = () > worker.RunWorkerAsync();; 1% complete, state = (1I, 1I) 2% complete, state = (1I, 2I) 3% complete, state = (2I, 3I) 4% complete, state = (3I, 5I) ...

memory management; rather, they will use the SORT_AREA_SIZE and HASH_AREA_SIZE parameters to decide how much RAM to allocate for various operations. In Oracle 10g and up, automatic PGA memory management is available to both connection types. It is important to properly set the SORT_AREA_SIZE and HASH_AREA_SIZE parameters when using shared server connections with Oracle9i.

So, the entire goal of automatic PGA memory management is to maximize the use of RAM while at the same time not using more RAM than you want. Under manual memory management, this was a virtually impossible goal to achieve. If you set SORT_AREA_SIZE to 10MB, when one user was performing a sort operation that user would use up to 10MB for the sort work area. If 100 users were doing the same, they would use up to 1,000MB of memory. If you had 500MB of free memory, the single user performing a sort by himself could have used much more memory, and the 100 users should have used much less. That is what automatic PGA memory management was designed to do. Under a light workload, memory usage could be maximized as the load increases on the system, and as more users perform sort or hash operations, the amount of memory allocated to them would decrease to reach the goal of using all available RAM, but not attempting to use more than physically exists.