The ALTER BUFFERPOOL statement is used to modify the characteristics or behavior of a buffer pool. There are a number of reasons to use the ALTER BUFFERPOOL statement, for example, to enable self-tuning memory.

The ALTER BUFFERPOOL statement can modify a buffer pool in the following ways:
  • Modify the size of the buffer pool on all members or on a single member
  • Enable or disable automatic sizing of the buffer pool
  • Add this buffer pool definition to a new database partition group
  • Modify the block area of the buffer pool for block-based I/O


This statement can be embedded in an application program or issued interactively. It is an executable statement that can be dynamically prepared only if DYNAMICRULES run behavior is in effect for the package (SQLSTATE 42509).


The privileges held by the authorization ID of the statement must include SYSCTRL or SYSADM authority.


Read syntax diagramSkip visual syntax diagramALTER BUFFERPOOLbufferpool-name IMMEDIATEDEFERREDMEMBERmember-numberSIZEnumber-of-pagesnumber-of-pagesAUTOMATICADD DATABASE PARTITION GROUPdb-partition-group-nameNUMBLOCKPAGESnumber-of-pagesBLOCKSIZEnumber-of-pagesBLOCKSIZEnumber-of-pages


Names the buffer pool. This is a one-part name. It is an SQL identifier (either ordinary or delimited). It must be a buffer pool described in the catalog.
Indicates whether or not the buffer pool size will be changed immediately.
The buffer pool size will be changed immediately. If there is not enough reserved space in the database shared memory to allocate new space (SQLSTATE 01657), the statement is executed as DEFERRED.
The buffer pool size will be changed when the database is reactivated (all applications need to be disconnected from the database). Reserved memory space is not needed; the database will allocate the required memory from the system at activation time.
MEMBER member-number
Specifies the member on which the size of the buffer pool is modified. An exception entry is created in the SYSCAT.BUFFERPOOLEXCEPTIONS catalog view. The member must be in one of the database partition groups for the buffer pool (SQLSTATE 42729). If this clause is not specified, the size of the buffer pool is modified on all members except those that have an exception entry in SYSCAT.BUFFERPOOLEXCEPTIONS.
Specifies a new size for the buffer pool, or enables or disables self tuning for this buffer pool.
The number of pages for the new buffer pool size. If the buffer pool is already a self-tuning buffer pool, and the SIZE number-of-pages clause is specified, the alter operation disables self-tuning for this buffer pool.
Enables self tuning for this buffer pool. The database manager adjusts the size of the buffer pool in response to workload requirements. If the number of pages is specified, the current buffer pool size is set to that value unless the deferred keyword is also specified, in which case the number of pages will be ignored. On subsequent database activations, the buffer pool size is based on the last tuning value that is determined by the self-tuning memory manager (STMM). The STMM enforces a minimum size for automatic buffer pools, which is the minimum of the current size and 5000 pages. To determine the current size of buffer pools that are enabled for self tuning, use the MON_GET_BUFFERPOOL routine and examine the current size of the buffer pools. The size of the buffer pool is found in thebp_cur_buffsz monitor element. When AUTOMATIC is specified, the MEMBER clause cannot be specified (SQLSTATE 42601).
ADD DATABASE PARTITION GROUP db-partition-group-name
Adds this database partition group to the list of database partition groups to which the buffer pool definition is applicable. For any member in the database partition group that does not already have the buffer pool defined, the buffer pool is created on the member using the default size specified for the buffer pool. Table spaces in db-partition-group-name may specify this buffer pool. The database partition group must currently exist in the database (SQLSTATE 42704).
NUMBLOCKPAGES number-of-pages
Specifies the number of pages that should exist in the block-based area. The number of pages must not be greater than 98 percent of the number of pages for the buffer pool, based on the NPAGES value in SYSCAT.BUFFERPOOLS (SQLSTATE 54052). Specifying the value 0 disables block I/O. The actual value of NUMBLOCKPAGES used will be a multiple of BLOCKSIZE.

NUMBLOCKPAGES is not supported in a Db2® pureScale® environment (SQLSTATE 56038).

BLOCKSIZE number-of-pages
Specifies the number of pages in a block. The block size must be a value between 2 and 256 (SQLSTATE 54053). The default value is 32.

BLOCKSIZE is not supported in a Db2 pureScale environment (SQLSTATE 56038).


  • Only the buffer pool size can be changed dynamically (immediately). All other changes are deferred, and will only come into effect after the database is reactivated.
  • If the statement is executed as deferred, although the buffer pool definition is transactional and the changes to the buffer pool definition will be reflected in the catalog tables on commit, no changes to the actual buffer pool will take effect until the next time the database is started. The current attributes of the buffer pool will exist until then, and there will not be any impact to the buffer pool in the interim. Tables created in table spaces of new database partition groups will use the default buffer pool. The statement is IMMEDIATE by default when that keyword applies.
  • There should be enough real memory on the machine for the total of all the buffer pools, as well as for the rest of the database manager and application requirements.
  • Syntax alternatives: The following syntax alternatives are supported for compatibility with previous versions of Db2 and with other database products. These alternatives are non-standard and should not be used.
    • DBPARTITIONNUM or NODE can be specified in place of MEMBER except when the DB2_ENFORCE_MEMBER_SYNTAX registry variable is set to ON.
    • NODEGROUP can be specified in place of DATABASE PARTITION GROUP