All about INITRANS

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All about INITRANS

The INITRANS setting controls Initial Transaction Slots (ITLs). A transaction slot is required for any session that needs to modify a block in an object. For tables INITRANS defaults to 1 for indexes, 2.
The MAXTRANS setting controls the maximum number of ITLs that a block can allocate (usually defaults to 255). If a block is sparsely populated then Oracle will dynamically increase the number of ITLs up to MAXTRANS.

ITL's, INITRANS and Block Waits

However, if the block has little or no free space then transactions will serialize waiting on a free ITL. This is one cause for data base block waits. By setting INITRANS to the number of expected simultaneous DML (data manipulation language - insert, update and delete) transaction for a single block, you can avoid serialization for ITL slots.
The maximum value suggested for INITRANS is 100 and settings over this size rarely improve performance. Therefore a setting of INITRANS to the average number of simultaneous DML users and setting MAXTRANS to 100 will most likely result in the best utilization of resources and performance. Remember, each ITL requires approximately 23 bytes in the block header.

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