What is stats gather in Oracle 11g?
When Oracle Database gathers system statistics, it analyzes system activity in a specified time period (workload statistics) or simulates a workload (noworkload statistics). The statistics are collected using the DBMS_STATS. GATHER_SYSTEM_STATS procedure. Oracle highly recommends that you gather system statistics.
Do we need to gather stats after index creation?
creating a new index – No. “Oracle Database now automatically collects statistics during index creation and rebuild”. adding a column – Maybe. If the column will be used in joins and predicates you probably want stats on it.
What is DBMS_STATS?
DBMS_STATS.GATHER_TABLE_STATS is what gathers the statistics that allow Oracle to make this determination. It tells Oracle that there are roughly 1 million rows in the table, that there are 3 distinct values for the issue_status column, and that the data is unevenly distributed.
What are statistics in Oracle?
Optimizer statistics are a collection of data that describe the database, and the objects in the database. These statistics are used by the Optimizer to choose the best execution plan for each SQL statement. Statistics are stored in the data dictionary, and can be accessed using data dictionary views such as.
What is granularity in Oracle?
The GRANULARITY parameter will allow you to decide the level of stats to be taken, GLOBAL as a whole object, PARTITION or SUBPARTITION. Options for the GRANULARITY parameter: ‘ALL’ – gathers all (subpartition, partition, and global) statistics. ‘AUTO’ – determines the granularity based on the partitioning type.
What is stale table in Oracle?
If a monitored table has been modified more than 10%, then these statistics are considered stale and gathered again.
What is a stale index?
Statistics are likely to be stale if the number of distinct values in an index has changed significantly. This can happen often or rarely, depending on the nature of the column being indexed. You can refresh cardinality statistics by calling the procedure SYSCS_UTIL.
What is global stats in Oracle?
Global statistics are generated by aggregating the synopses from each partition, thus eliminating the need for the full table scan (see Figure below). When a new partition is added to the table you only need to gather statistics for the new partition.
What does compute statistics do in Oracle?
COMPUTE STATISTICS instructs Oracle Database to compute exact statistics about the analyzed object and store them in the data dictionary. When you analyze a table, both table and column statistics are collected.
How do I create an index in Oracle?
You cannot create a bitmap join index on an index-organized table or a temporary table.
What is index and different types of indexes in Oracle?
b-tree index. The most common index type is the b-tree index.
When should I use an oracle index?
– The locking parameter is ignored when SYNC_INDEX is invoked without an index name. – The locking parameter cannot be communicated for automatic synchronizations (that is, sync on commit or sync every ). – When the locking mode is LOCK_WAIT, the mode waits forever and ignores the maxtime setting if it cannot get a lock.
Does Oracle use my index or not?
In sum, the Oracle optimizer should immediately see a new index and begin using it immediately, invalidating all SQL that might benefit from the index. When Oracle does not use an index, you can force him to use the index with diagnostic tools. Testing to force Oracle to use an index is easy.