How an Insert Statement Processed in DB2
How an Insert Statement Processed in DB2
When SQL statements use INSERT to place new information in a table, an INSERT search algorithm first searches the Free Space Control Records (FSCRs) to find a page with enough space. However, even when the FSCR indicates a page has enough free space, the space may not be usable because it is reserved by an uncommitted DELETE from another transaction. To ensure that uncommitted free space is usable, you should COMMIT transactions frequently. The setting of the DB2MAXFSCRSEARCH registry variable determines the number of FSCRs in a table that are searched for an INSERT. The default value for this registry variable is five. If no space is found within the specified number of FSCRs, the inserted record is appended at the end of the table. To optimize INSERT speed, subsequent records are also appended to the end of the table until two extents are filled. After the two extents are filled, the next INSERT resumes searching at the FSCR where the last search ended.