The following configuration parameters affect fast recovery:
The OFF_RECVRY_THREADS and ON_RECVRY_THREADS configuration parameters specify the number of recovery threads, respectively, that operate when the database server performs a cold restore, warm restore, or fast recovery. The setting of OFF_RECVRY_THREADS controls cold restores, and the setting of ON_RECVRY_THREADS controls fast recovery and warm restores.
With fuzzy checkpoints, fast recovery might take longer than with full checkpoints. To improve the performance of fast recovery, increase the number of fast-recovery threads with the ON_RECVRY_THREADS configuration parameter. The number of threads should usually match the number of tables or fragments that are frequently updated to roll forward the transactions recorded in the logical log.
Another estimate is the number of tables or fragments that experience frequent updates. On a single-CPU host, the number of threads should be no fewer than 10 and no more than 30 or 40. At a certain point, the overhead that is associated with each thread outweighs the advantages of parallel threads.
A warm restore takes place concurrently with other database operations. To reduce the impact of the warm restore on other users, you can allocate fewer threads to it than you would to a cold restore. However, to replay logical-log transactions in parallel during a warm restore, specify more threads in the ON_RECVRY_THREADS parameter.
The PLOG_OVERFLOW_PATH configuration parameter specifies the location of a disk file (named plog_extend.servernum) that the database server uses if the physical log file overflows during fast recovery.
The database server removes the plog_extend.servernum file when the first checkpoint is performed during a fast recovery.
For situations when you are using fuzzy checkpoints and need faster recovery performance, you can use either or both of the following configuration parameters:
You can use either parameter or both when using fuzzy checkpoints. The default value for both parameters is 0 (off). Set them to 1 (on) to use them.
The extra physical logging that occurs when the database server uses the FAST_RESTART_PHYSLOG configuration parameter affects runtime performance. If you do not want to sacrifice runtime performance, you can use the FAST_RESTART_CKPT_FUZZYLOG configuration parameter to reduce some recovery time.
FAST_RESTART_PHYSLOG takes effect immediately after you enable it. However, if the database server fails before the next checkpoint performs, maximum fast-recovery performance does not occur because the database server did not log all of the fuzzy updates in the checkpoint intervals.
For more information on these parameters, see the IBM Informix: Dynamic Server Administrator's Reference and information on fast restart recovery options in the IBM Informix: Dynamic Server Administrator's Guide.
Enterprise Edition Home | Express Edition Home | [ Top of Page | Previous Page | Next Page | Contents | Index ]