What is DB2 table reorg?

What is DB2 table reorg?

To keep it simple: REORG is a database operation that is executed in DB2 to reorganize the table spaces or index spaces. The purpose of the reorganization is data clustering. Basically classic REORG creates a temporary copy of the table / index, then replaces the original one with the organized copy.

What is online reorg in DB2?

Online Reorg is an availability enhancement to DB2 introduced in DB2 Version 5. It increases availability of a tablespace and/or index while it is being reorganised. The reorganisation of an object necessarily consists of the destruction of an object and its rebuilding in reorganised form.

What is the need of using reorg utility?

The REORG TABLESPACE online utility reorganizes a table space to improve access performance and to reclaim fragmented space. In addition, the utility can reorganize a single partition or range of partitions of a partitioned table space. You can specify the degree of access to your data during reorganization.

What is offline reorg in DB2?

There are four phases in a CLASSIC or offline table reorganization operation: SORT – During this phase, if an index was specified on the REORG TABLE command, or a clustering index was defined on the table, the rows of the table are first sorted according to that index.

Why do we use Runstats in Db2?

RUNSTATS is a Db2® utility that scans a table space or indexes to gather information about space utilization and index efficiency. The information gathered is stored in the Db2 system tables and used by the SQL optimizer to select the best access paths during the bind process.

What is the use of reorg and Runstats in Db2?

runstats is for collecting indexes and tables statistics information which to enable the DB2 optimizer to generate efficient access plan. reorgs is for reorganizing tables and indexes.

What is Shrlevel change?

For reorganizing a table space, or a partition of a table space, the SHRLEVEL option lets you choose the level of access that you have to your data during reorganization. REORG with SHRLEVEL CHANGE reloads the reorganized data into a shadow copy of the area that is being reorganized.

Which utility is used to update the data related to tablespaces and indexes in system catalog tables?

DB2 records these statistics in the DB2 catalog and uses them to select access paths to data during the bind process. The STOSPACE online utility updates DB2 catalog columns that indicate how much space is allocated for storage groups and related table spaces and indexes.

How does reorg work in DB2?

If the table space is defined by storage groups, Db2 allocates space, and you cannot alter data set definitions while a REORG job is in process. Db2 deletes and redefines the necessary data sets to reorganize the object. You can temporarily pause REORG TABLESPACE. Db2 estimates how many records are to be sorted.

What is the use of reorg and Runstats in DB2?

What does the runstats command do in IBM DB2?

IBM Db2. RUNSTATS command. The RUNSTATS command updates statistics in the system catalog about the characteristics of a table, associated indexes, or statistical views. These characteristics include number of records, number of pages, and average record length.

When do I need to do a reorg in DB2?

REORG is used to help DB2 point to accurate data (ie, indexes should become aware of fresh data and no longer include deleted data), as well as “collapse” empty page space created by deletion of data and/or indexes.

How to generate and run reorg and runstats scripts?

Reorg and runstats are recommended on these tables. You can create reorg and runstats scripts to make DB2® performance tuning easy. To generate and run reorg and runstats scripts: Log in as the DB2 administrator, and connect to the database.

Where does the summary information in DB2 come from?

Gathers summary information about the characteristics of the data in table spaces and indexes. This information is recorded in the DB2 catalog, and is used by DB2 to select access paths to data during the bind process.