2. Vector Concepts : Table Structures : Data Storage Format
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Data Storage Format
A database consists of multiple files and can reside in multiple locations. Tables can also be spread across multiple locations.
Updates, inserts, and deletes to the data and the layout of the data in the data files are stored as log information on HDFS in II_HDFSDATA/ingres/data/vectorwise/dbname/wal). The data files and the wal directory must be considered together as files that represent the database.
The data files consist of a number of blocks, which can be seen as the equivalent of pages. Each block contains possibly compressed data from one or more attributes. The size of the block can be configured with the [cbm] block_size before creating a database.
Also, for better sequential access performance, multiple blocks from the same column can be stored contiguously in a block group. The size of this group can be configured with the [cbm] group_size parameter (see  group_size).
Database size is unlimited because data can be spread across multiple disks. If a table or a column is dropped, its corresponding file or files are deleted and the disk space is reclaimed by the operating system.
Note:  Due to concurrent transactions, the system can internally still contain references to a table or a column even when it is dropped, so the effect of dropping a table or column may not be seen immediately but only after all concurrent transactions have ended.