| Measurement |
Description |
Measurement
Unit |
Interpretation |
| Redo_buffer_retries
|
This indicates
the number of attempts to allocate space in the redo buffer. A value
other then 0 indicates that the redo writer is falling behind. This
could be caused by log switches or checkpoints. |
Number
|
By adjusting the LOG_CHECKPOINT_INTERVAL and LOG_CHECKPOINT_TIMEOUT
parameters in the init.ora, you will be able to minimize the number of
checkpoints. From Oracle 9i onwards however, the LOG_CHECKPOINT_INTERVAL parameter is supported only for ensuring backward compatability with previous versions of Oracle. The recommended equivalent in case of Oracle 9i therefore is FAST_START_MTTR_TARGET. You can also increase the number of LGWR writers. These
parameters are new in Oracle8 and are defined in the init.ora
parameters LGWR_IO_SLAVES and ARCH_IO_SLAVES. However, note that both these parameters are obsolete from Oracle 8i onwards.
|
| Redo_log_space_requests
|
The active log
file is full and Oracle is waiting for disk space to be allocated for
the redo log entries. Space is created by performing a log switch. |
Number
|
Small Log files in relation to the size of the SGA or the commit rate
of the work load can cause problems. When the log switch occurs,
Oracle must ensure that all committed dirty buffers are written to
disk before switching to a new log file. If you have a large SGA full
of dirty buffers and small redo log files, a log switch must wait for
DBWR to write dirty buffers to disk before continuing.
|
| Redo_entries
|
This statistic
increments each time redo entries are copied into the redo log buffer.
(ie. The number of attempts to allocate space in the redo) |
Number
|
|
| Pct_log_space_requests
|
This indicates
the percentage of log space requests. |
Percentage
|
If the number is greater than 1%, you should increase the size of the
Redo Log buffer. I would also check the checkpoint and size of
the online redo log file.
|
| Log_space_waits
|
This measure
indicates the number of times wait has happened to acquire a log
buffer. |
Number
|
If the Log Buffer space waits exist, consider increasing the size
of the redo log. Also I would check the speed of the disk that
the Online Redo Log files are in.
|
| Redo_nowait_pct |
Indicates the percentage of redo entries for which there was space immediately available in the redo log. |
Percent |
A high value is typically desired for this measure. A low value indicates that many redo entries are waiting for space to become available in the redo logs.
Frequent, or slow log switches may be contributing to waits for redo log space. If you are switching logs frequently (e.g. more than once every 15 minutes) this may be improved by increasing the size of the online redo logs.
If the log switches are not frequent, check the disks the redo logs reside on to see if log switches are taking a long time due to a slow I/O system. If the I/O system is overloaded, either move the redo logs to disks with less activity, place the logs on dedicated disks or faster devices. |