Oracle Internals Notes

Small Redo Entries

Prior to release 8.1, the use of a redo copy latch to copy a redo record into the log buffer was conditional on the size of the entry. If the redo entry was less than the number of bytes specified by the _log_small_entry_max_size parameter then a redo copy latch would not be taken, and the copy would be performed while retaining the redo allocation latch. This parameter defaulted to 800 bytes up to the early releases of Oracle 7.3, and to 80 bytes thereafter. Copies performed under the redo allocation latch were reported in the redo small copies statistic, and it was not uncommon for this to represent almost all redo entries. However, it was a common tuning practice to set the parameter to 0 bytes to prevent small copies entirely, and thus minimize the load on the critical redo allocation latch. From release 8i, this parameter no longer exists, and all copies are performed under a redo copy latch.

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12-Oct-2007 22:22
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