NDB Cluster Configuration Files The UNDO index buffer, whose size is set by this parameter, is used during local checkpoints. The NDB  storage engine uses a recovery scheme based on checkpoint consistency in conjunction with an operational REDO log. To produce a consistent checkpoint without blocking the entire system for writes, UNDO logging is done while performing the local checkpoint. UNDO logging is activated on a single table fragment at a time. This optimization is possible because tables are stored entirely in main memory. The UNDO index buffer is used for the updates on the primary key hash index. Inserts and deletes rearrange the hash index; the NDB storage engine writes UNDO log records that map all physical changes to an index page so that they can be undone at system restart. It also logs all active insert operations for each fragment at the start of a local checkpoint. Reads and updates set lock bits and update a header in the hash index entry. These changes are handled by the page-writing algorithm to ensure that these operations need no UNDO logging. This buffer is 2MB by default. The minimum value is 1MB, which is sufficient for most applications. For applications doing extremely large or numerous inserts and deletes together with large transactions and large primary keys, it may be necessary to increase the size of this buffer. If this buffer is too small, the NDB storage engine issues internal error code 677 ( Index UNDO buffers overloaded ). It is not safe to decrease the value of this parameter during a rolling restart. This parameter sets the size of the UNDO data buffer, which performs a function similar to that of the UNDO index buffer, except the UNDO data buffer is used with regard to data memory rather than index • UndoDataBuffer Important 4114 Version (or later) NDB 8.0.13 Type or units unsigned Default 2M Range 1M - 4294967039 (0xFFFFFEFF) Restart Type N (NDB 8.0.13) Version (or later) NDB 8.0.13 Type or units unsigned Default 16M Range 1M - 4294967039 (0xFFFFFEFF) Restart Type N (NDB 8.0.13)