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You can choose instance recovery time following a crash by specifying the mean time to recover (MTTR) from the failure, in seconds. You use the FAST_START_MTTR_TARGET initialization parameter for this purpose, as explained in 16. If you choose a short MTTR, Oracle will accommodate you, but it ll most likely have to perform a lot more incremental checkpoints than if you chose a longer MTTR. Increasing checkpointing would affect instance performance, because of the excessive writing to data files. The V$MTTR_TARGET_ADVICE view shows the tradeoff between a lower instance recovery time and additional physical writes. The view provides information about physical writes, which helps you determine the ideal MTTR for your instance. This view is the basis for Oracle s MTTR Advisor, which helps you evaluate various MTTR sizes by showing the estimated impact of each setting on extra physical writes: SQL> SELECT mttr_target_for_estimate, estd_cache_writes, estd_total_writes,estd_total_ios FROM V$MTTR_TARGET_ADVICE; MTTR_TARGET_FOR_EST ESTD_CACH_WRIT ESTD_TOT_WRITES ESTD_TOTAL_IOS ------------------------------------------------------------------53 9103239 9717060 677755152 83 6558125 7171946 675210038 114 6369149 6982970 675021062 145 6259821 6873642 674911734 176 6194878 6808699 674846791 SQL>

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The V$INSTANCE_RECOVERY view monitors the number of blocks set as the target and records ongoing estimates of the MTTR. The view can tell you what the current MTTR is and what the estimated MTTR is, based on instance activity. Here s a typical query using the V$INSTANCE_ RECOVERY view: SQL> SELECT recovery_estimated_ios, /*no. of dirty buffers in the buffer cache*/ 2 actual_redo_blks, /* no. of redo blocks needed for recovery */ 3 target_redo_blks, /*target no. of redo blocks to be processed*/ 4 target_mttr, /* mean time to recover target value */ 5 estimated_mttr /* current estimated mean time to recover */ 6* FROM V$INSTANCE_RECOVERY; REC_EST_IOS ACTUAL_REDO TARGET_REDO TARGET_MTTR ESTIMATED_MTTR ---------------- ---------------- ---------------- ----------983 2422 18432 60 38 SQL>

The following function performs all notifications and process terminations in the script. It is called with seven sequentially numbered parameters. The positional variables are somewhat difficult to understand and their values could have been assigned to more meaningfully named variables before they were used, for ease of debugging later. To streamline the script a little, I didn t do this.

The preceding query shows that the target MTTR is 60 seconds, but based on current instance activity, you can expect your actual MTTR to be less than that (38 seconds). The OPTIMAL_LOGFILE_SIZE column of the V$INSTANCE_RECOVERY view helps you size your redo logs properly, by showing the optimal redo log size for the MTTR size that you choose. Oracle recommends that all your online redo logs be at least as large as indicated by the OPTIMAL_LOGFILE_ SIZE column value.

The V$RECOVER_FILE view provides information on all files that need recovery. Following is the structure of the V$RECOVER_FILE view: SQL> DESC V$RECOVER_FILE Name Null Type ------------------ ------- -----------FILE# NUMBER ONLINE VARCHAR2(7) ONLINE_STATUS VARCHAR2(7) ERROR VARCHAR2(18) CHANGE# NUMBER TIME DATE SQL>

This chapter has discussed how you can implement special member functions for managed types. Even though many special member functions of managed types have similar counterparts in the native world, there are subtle but significant differences. At construction time, virtual methods of managed objects are dispatched to overridden implementations even though this can cause access to parts of an object that are not yet initialized. To reduce this danger, constructors for fields of managed types are called before the base class constructor is called. There are also differences regarding object destruction. The GC is responsible for reclaiming memory. Since its timing is nondeterministic, cleanup of the resources held by an object is decoupled from memory cleanup. To implement code that cleans up an object s resources in a deterministic manner, C++/CLI allows you to implement a destructor. This destructor is

The V$RECOVERY_FILE_DEST view contains information about the amount of used and free space in the flash recovery area, among other things. You ve seen how you must set values for both the DB_RECOVERY_FILE_DEST and the DB_RECOVERY_FILE_DEST_SIZE parameters to use the flash recovery area inside your database.