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In current releases of the database, instead of waiting for the commit to complete, which may take measurable time since a commit involves a physical write a physical IO to the redo log files stored on disk, you may have the commit performed in the background, without waiting for it That comes with the side-effect that your commit is no longer assured to be durable That is, your application may get a response back from the database that the asynchronous commit you submitted was received, other sessions may be able to see your changes, but later find that the transaction you thought was committed was not This situation will occur only in very rare cases and will always involve a serious failure of the hardware or software.

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It requires the database to be shutdown abnormally in order for an asynchronous commit to not be durable, meaning the database instance or computer the database instance is running on would have to suffer a complete failure So, if transactions are meant to be durable, what is the potential use of a feature that might make them possibly not durable Raw performance When you issue a COMMIT in your application, you are asking the LGWR process to take the redo you ve generated and ensure that it is written to the online redo log files Performing physical IO, which this process involves, is measurably slow; it takes a long time, relatively speaking, to write data to disk.

// random results will vary! val it : seq<int * int> = seq [(814, 662596); (686, 470596); (242, 58564)]

So, a COMMIT may well take longer than the DML statements in the transaction itself! If you make the COMMIT asynchronous, you remove the need to wait for that physical I/O in the client application, perhaps making the client application appear faster especially if it does lots of COMMITs This might suggest that you d want to use this COMMIT WRITE NOWAIT all of the time after all isn t performance the most important thing in the world No, it is not Most of the time, you need the durability achieved by default with COMMIT When you COMMIT and report back to an end user we have committed, you need to be sure that the change is permanent It will be recorded in the database even if the database/hardware failed right after the COMMIT.

If you report to an end user that Order 12352 has been placed, you need to make sure that Order 12352 was truly placed and persistent So, for most every application, the default COMMIT WRITE WAIT is the only correct option (note that you only need say COMMIT the default setting is WRITE WAIT) When would you want to use this new capability to commit without waiting then Three scenarios come to mind: A custom data load program It must be custom, since it will have additional logic to deal with the fact that a commit might not persist a system failure An application that processes a live data feed of some sort, say a stock quote feed from the stock markets that inserts massive amounts of time-sensitive information into the database.

Some of the most general operators supported by most F# data structures are the fold, fold_left, and fold_right operators. These apply a function to each element of a collection and accumulate a result. For fold_left and fold_right, the function is applied in left-to-right or right-toleft order, respectively. If the name fold is used, then typically the ordering is left to right. Both functions also take an initial value for the accumulator. For example: > List.fold_left (fun acc x -> acc + x) 0 [4; 5; 6];; val it : int = 15 > Seq.fold (fun acc x -> acc + x) 0.0 [4.0; 5.0; 6.0];; val it : float = 15.0 > List.fold_right (fun x acc -> min x acc) [4; 5; 6; 3; 5] System.Int32.MaxValue;; val it : int = 3 The following are equivalent, but no explicit anonymous function values have been used: > List.fold_left (+) 0 [4; 5; 6];; val it : int = 15 > Seq.fold (+) 0.0 [4.0; 5.0; 6.0];; val it : float = 15.0 > List.fold_right min [4; 5; 6; 3; 5] System.Int32.MaxValue;; val it : int = 3 If used carefully, the various fold_right operators are pleasantly compositional, because they let you apply a selection function as part of the accumulating function: > List.fold_right (fst >> min) [(3, "three"); (5, "five")] System.Int32.MaxValue;; val it : int = 3 At the time of writing, the F# library also includes more direct accumulation functions such as Seq.sumByFloat and Seq.sumByInt. These use a fixed accumulation function (addition) with a fixed initial value (zero).