Movatterモバイル変換

• Variable-length columns of Disk Data tables take up a fixed amount of space. For each row, this is equal to the space required to store the largest possible value for that column.

  For general information about calculating these values, seeSection 13.7, “Data Type Storage Requirements”.

  You can obtain an estimate the amount of space available in data files and undo log files by querying the Information SchemaFILES table. For more information and examples, seeSection 28.3.15, “The INFORMATION_SCHEMA FILES Table”.

  Note

  TheOPTIMIZE TABLE statement does not have any effect on Disk Data tables.

• In a Disk Data table, the first 256 bytes of aTEXT orBLOB column are stored in memory; only the remainder is stored on disk.

• Each row in a Disk Data table uses 8 bytes in memory to point to the data stored on disk. This means that, in some cases, converting an in-memory column to the disk-based format can actually result in greater memory usage. For example, converting aCHAR(4) column from memory-based to disk-based format increases the amount ofDataMemory used per row from 4 to 8 bytes.

Starting the cluster with the--initial option doesnot remove Disk Data files. You must remove these manually prior to performing an initial restart of the cluster.