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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 overflow in Db2?
A table read overflow occurs when DB2 attempts to read the row from its original location, then discovers the pointer and has to go read the row from its new location. Read overflows are particularly expensive because DB2 is now forced to do double the logical read I/O and probably double the physical I/O as well.
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 Release commit does in DB2?
In that case, RELEASE(COMMIT) releases a lock that Db2 must acquire again immediately. RELEASE(DEALLOCATE) holds the lock until the application ends, avoiding the processing that is required to release and acquire the lock several times.
What is reorg in database?
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. This operation reconstructs the data in the table spaces or index spaces, so that the data is unfragmented and physically continuous.
How do you calculate percentages in DB2?
1. Percentage in DB2
- (PERSON_SPEND / TOTAL_SPEND) * 100 AS PERC,
- CAST((PERSON_SPEND / TOTAL_SPEND) * 100 AS DECIMAL(3,3)) AS PERC,
- DECIMAL(PERSON_SPEND * 100 / TOTAL_SPEND,5,2) AS PERC,
When should I run my Runstats?
When to Run Runstats in DB2
- When a table is loaded.
- When an index is created.
- When a tablespace is reorganized.
- When there have been extensive updates, deletions, or insertions in a tablespace.
- After the recovery of a tablespace to a prior point in time.
What does Runstats do 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.
When do you use runstats in DB2 10.5?
DB2 uses a metric on how much data in a table has changed to decide if runstats are needed, and I’ve seen it make some major misses, even with DB2 10.5. Often I’ll let automatic stats run, but then have a weekly full scripted stats or have a script that looks for tables with old runstats and only does runstats on them.
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.
When to run runstats on a specific table?
Often to deal with a performance problem, we may need to run a specific set of runstats on a specific table. This can include using sampling as tables become large and runstats time becomes too long. It can include doing runstats on groups of columns, or a number of other things.