What is Explain plan in Oracle
The EXPLAIN PLAN results help you understand the optimizer decisions, such as why the optimizer chose a nested loops join instead of a hash join, and they help you understand the performance of a query. You can use the results to determine whether the optimizer chooses a specific execution plan, such as a nested loops join.
What is explain plan in SQL Developer
The SELECT, UPDATE, INSERT, and DELETE statements execution plans are displayed by the EXPLAIN PLAN statement. An execution plan is the sequence of operations Oracle performs to run a statement. The row source tree is the core of the execution plan.
What is cost in Explain plan in Oracle
Cost is the estimated amount of work the plan will perform. All other things being equal, a query with a higher cost will use more resources and thus take longer to run. A higher cardinality => youre going to fetch more rows => youre going to do more work => the query will take longer. Mar 22, 2017
What is Tkprof in Oracle with example
TKPROF takes longer to process a large trace file if the EXPLAIN option is used. RECORD. TKPROF determines execution plans by issuing the EXPLAIN PLAN statement after connecting to Oracle with the user and password specified in this parameter. The specified user must have CREATE SESSION system privileges.
How do I use explain plan in Toad
Type your SQL query into Toads SQL Editor by selecting Database > SQL Editor, then press Ctrl E to run the querys Explain Plan. If a Plan Table doesnt already exist in your database, Toad will prompt you to create one.18 September 2018
What is reduce cost in Explain plan in Oracle
This plan is more efficient because two indexes are used to satisfy the predicates in the parent query, returning only a small number of employee_ids, which are then used to access the orders table through an index. The cost of the plan is reduced by rewriting the SQL statement to use an EXISTS.
How do you tune a query in explain plan
The approach I generally take is:
- Run the questioned SQL statement,
- Find the actual plan by searching for “dbms_xplan,”
- Compare the difference between the estimated and actual rows (cardinality).
- In general, where you conceptually believe the plan should go first, consider whether you can speed up the process by creating an index.
How can I improve my Oracle query performance
On a partitioned table, each partition has its own set of index tables; technically, there are multiple indexes, but the results from each are combined as necessary to produce the final result set. Partitioning your data and creating local partitioned indexes can improve query performance.
How do I know if execution plan has changed
The view GV$SQL contains the most recent SQL, but if you cant find the query in this view, try DBA_HIST_SQLTEXT instead. Next, you need to find the SQL_ID for the relevant query. If you cant find the query in this view, try DBA_HIST_SQLTEXT.
How do I change the execution plan in Oracle
Perform the following steps:
- Log in as the system user when Enterprise Manager DB Control is open.
- choosing the Server tab
- Select SQL Plan Control from the list of query optimizers.
- Select the tab for the SQL Plan Baseline.
- Choose the link FALSE for Capture SQL Plan Baselines under Settings.
What are different types of joins in Oracle
There are 4 different types of Oracle joins:
- Oracles INNER JOIN, also known as a “simple join,”
- Oracle LEFT OUTER JOIN (also known as LEFT JOIN occasionally)
- Oracle RIGHT OUTER JOIN (also known as RIGHT JOIN occasionally)
- Oracle FULL OUTER JOIN (also known as FULL JOIN occasionally)
What are different types of indexes in Oracle
- Characteristics of the index.
- Indexes for B-Trees.
- Indexes in bitmaps.
- Indexes Based on Function.
- Indexes for application domains.
- Index Keeping.
What is cardinality in Oracle explain plan
You want to look for cases where the optimizer sees 5 rows (cardinality) but there are actually 50,000 rows (cardinality), as this is the number of rows the optimizer guesses will be processed for a plan step. If the stats are outdated, missing, or incomplete, then this can be wildly incorrect.
What does autotrace do in Oracle
The AUTOTRACE report includes both the optimizer execution path and the SQL statement execution statistics. SET AUTOTRACE TRACEONLY is similar to SET AUTOTRACE ON but suppresses the printing of the users query output, if any.
How do you delete duplicate records in Oracle
Using the Standard Query Language, or SQL, search for the records you want to delete, such as “delete from names where name = Alan,” and then enter “commit” to make the command effective. To delete duplicate records in Oracle, first make sure the records are indeed duplicates.
What are the different methods to access SQL plan
An access path is a technique used by a query to retrieve rows from a row source.
8 Optimizer Access Paths
- Overview of Access Paths.
- Access Paths to Tables.
- Access Paths to the B-Tree Index.
- Index Access Paths for Bitmaps.
- Access Paths for a Table Cluster.
Which columns should be indexed in Oracle
A column should generally have an index created on it if any of the following conditions apply: the column is frequently queried; there is a referential integrity constraint on it; or the column has a unique key integrity constraint.
What is hash join in Oracle
Oracle accesses one table (typically the smaller of the joined results) in a HASH join and creates a hash table on the join key in memory. It then scans the other table in the join (typically the larger one) and probes the hash table for matches to it.