What is Pctfree and Pctused setting?
PCTFREE is set to 20 to allow enough room for rows that increase in size as a result of updates. PCTUSED is set to 40 so that less processing is done during high update activity, thus improving performance.
What is Pctused?
PCTUSED is a block storage parameter used to specify when Oracle should consider a database block to be empty enough to be added to the freelist. Oracle will only insert new rows in blocks that is enqueued on the freelist.
What is Initrans and Maxtrans?
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).
What is Pctfree in db2?
The PCTFREE clause specifies the percentage of each data page in a table space that is left free when loading or reorganizing the data. For example, the default value for table spaces PCTFREE 5, which means that 5% of each data page is kept free when you load or reorganize the data.
What is pct increase Oracle?
The PCTINCREASE parameter in the STORAGE clause determines the degree to which Oracle will automatically increase the size of subsequent extent allocations. This value is expressed as an integer percentage, and is applied to the then-current value of the NEXT parameter.
How do I find a high-water mark?
Hydrologists often visit streams after a large storm to check for high-water marks. If, for example, records show that stream stage reached 17 feet during a storm, a high-water mark will show the hydrologist what a stage of 17 feet means in terms of how high the water was on the riverbanks and surrounding land.
What is Freepage in Db2?
Use the FREEPAGE clause to specify how often Db2 leaves a full page of free space when loading data or when reorganizing data. For example, if you specify FREEPAGE 10, Db2 leaves every tenth page free.
What is the difference between PCT_free and pctused?
For example, with PCTUSED=60, all database blocks that have less than 60 percent data will be on the free list, as well as other blocks that dropped below PCT_USED and have not yet grown to PCT_FREE. Once a block deletes a row and becomes less than 60 percent full, the block goes back on the free list.
How do I adjust the pctfree and pctused settings?
The script in Listing 1 (pctused.sql) allows you to adjust the setting for PCTFREE and PCTUSED as a function of the number of rows that you want to store between I/Os. Remember the rule: The lower the value for PCTUSED, the less I/O your system will have at insert time, and the faster your system will run.
What is the default value of pctfree?
PCTFREE: Minimum percentage of free space in a block; null for partitioned tables. PCTFREE is defined as the value which keep free in a block for future rows present in the block to avoid row chaining. Default value of PCTFREE is 10. If you set less than that then depend upon update, it may cause row chaining in Oracle.
When should the pctused value be set above 40?
In short, the value for PCTUSED should only be set above 40 when the database is short on disk space, and it must make efficient re-use of data block space. It should now be very clear that you need to consider the average row length when customizing the values for PCTFREE and PCTUSED.