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Overview of transactions and versioning
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How Adaptive Server IQ keeps track of versions
Adaptive Server IQ assigns a version identifier to each database object that
exists in the metadata, and that has a life span beyond a single command. IQ
uses these version identifiers to ensure that writes to any database object are
always based on the latest version of the object. It keeps each active version of
a database object on disk.
When an older version is no longer needed by active transactions, Adaptive
Server IQ drops it from the database. A version is needed until the transactions
using it do one of the following:
•Commit
• Roll back
•Issue a
RELEASE SAVEPOINT command releasing that version
For information on defining, releasing, and rolling back to savepoints, see
“Savepoints within transactions”.
Versioning of temporary tables
A temporary table that is created in the database is called a global temporary
table. A global temporary table is accessible to all users with the appropriate
permissions. Each user has his or her own instance of the table, however; only
one user ever sees a given set of rows. By default, a global temporary table is
deleted at the next
COMMIT. You can override this default, by specifying ON
COMMIT PRESERVE ROWS
when you create the temporary table.
A local temporary table is declared rather than created in the database. Only
one user sees any of the rows in a local temporary table. The table is dropped
when that user disconnects. When you declare a local temporary table,
Adaptive Server IQ issues a savepoint instead of committing the transaction
automatically, as it would for a data definition operation on any other type of
table.
For purposes of versioning, Adaptive Server IQ makes no distinction between
base tables (main database tables) and global temporary tables. Because the
data in any temporary table is accessible to only one user, there will never be
more than one write transaction open for a temporary table.