15.00 - UNCOMPRESS - Teradata Database

Teradata Database Utilities

Product
Teradata Database
Release Number
15.00
Content Type
Configuration
Publication ID
B035-1102-015K
Language
English (United States)
Last Update
2018-09-25

UNCOMPRESS

Purpose  

Uncompresses specified types of data in specified databases and tables, or shows an estimate of what results would be if tables were uncompressed. If data of one of the specified types is subsequently added to the table or database, it will not be compressed.

Uncompression uses the algorithm specified by the CompressionAlgorithm setting in DBS Control.

Syntax  

 

Syntax Element

Description

/Y

Prevents Ferret from displaying a confirmation message.

  table_unique

Unique identifier of the table for which data blocks will be uncompressed.

The table to be uncompressed can be uniquely identified in either of two ways:

  • Specify the name of the database to which the table belongs and the table name, separated by a period. The names individually or together must be delimited. The following formats are valid:
  • "database_name.table_name"
  • 'database_name.table_name'
  • "database_name"."table_name"
  • 'database_name'.'table_name'
  • "database_name.*"
  • 'database_name.*'
  • "database_name"."*"
  • 'database_name'.'*'
  • The asterisk denotes all tables in the given database.

  • Specify the unique numeric identifier of the table, which consists of two numeric values separated by a space. The table identifier consists of the first two numeric values returned by the “TABLEID” command. These two numbers are common to all subtables that comprise the table.
  • Note: The format of the input numbers depends on the current radix setting, which is displayed by the “RADIX” command.

    PRIMARY

    Uncompresses all primary base and CLOB data within specified database or table.

    FALLBACK

    Uncompresses all fallback base and CLOB data within specified database or table.

    FALLBACKANDCLOBS

    Uncompresses all fallback base and CLOB data, and all primary CLOB data within specified database or table.

    WITHOUT CLOBS

    Uncompresses all data except CLOB data within specified database or table.

    ONLY CLOBS

    Uncompresses only data in CLOB subtables. Other table DBs are not affected.

    ESTIMATE
    E

    Estimates data block (DB) sizes that would exist after an uncompress operation is performed, and estimates the CPU usage (time per DB) that would be required. Does not uncompress any data.

    Multiply the Table Size Factor shown in the output by the current table size to determine the estimated table size after an uncompress operation.

    Note: Estimates are most accurate when the table DB size is at or near the size defined by DATABLOCKSIZE (optionally specified when the table was created or altered), or defined by the PermDBSize setting in DBS Control if no DATABLOCKSIZE was specified for the table.

    Usage Notes

    The UNCOMPRESS command is part of the block-level compression (BLC) feature of Teradata Database.

    BLC enables data compression at the data block (DB) level of the Teradata Database file system. Compression reduces the amount of storage required for a given amount of data. The BlockLevelCompression field of DBS Control enables and disables BLC.

    BLC can be enabled or disabled system-wide, or for various categories of tables. For Permanent data, only primary, fallback, and CLOB subtables, and join and hash indexes are eligible for BLC. Secondary indexes on primary rows are never compressed, but fallback copies of secondary indexes can be compressed to save space.

    The UNCOMPRESS command consumes storage space as it uncompresses data. To ensure sufficient space is available after an uncompress command completes, use the UncompressReservedSpace setting in DBS Control to specify the amount of space to reserve. The decompression operation stops when the available free space falls below the reserved amount. The table undergoing decompression at the time may remain in a partially compressed state. This will not affect the functioning of the table or database. To resume decompression, free up some storage space, or lower the value of UncompressReservedSpace then reissue the UNCOMPRESS command.

    Ferret logs the beginning and end of UNCOMPRESS operations. If the database is reset during the operation, the decompression operation continues as part of the recovery process after the database restarts. However, decompression will continue and complete only on the table that was in the process of being decompressed at the time of the reset. The rest of the database will remain in the state it was prior to the reset.

    Only one instance of the UNCOMPRESS command is allowed to run at any time on the system. If you receive an error when you issue the COMPRESS or UNCOMPRESS command, and you are certain there is no other instance of either command currently running, use the RESETBLCTSKCNT command to reset the count of running COMPRESS and UNCOMPRESS tasks to zero.

    The command progress percentage reported by the INQUIRE command can change unexpectedly if the table being uncompressed is being modified concurrently by another process.

    The PermDBSize and JournalDBSize settings in DBS Control apply to the uncompressed size of these types of DBs.

    If you receive an error when you issue the COMPRESS or UNCOMPRESS command, and you are certain there is no other instance of either command currently running, use the RESETBLCTSKCNT command to reset the count of running COMPRESS and UNCOMPRESS tasks to zero.

    Related Topics

     

    For more information on…

    See…

    DBS Control compression settings

    Chapter 11: “DBS Control (dbscontrol).”

    COMPRESS command

    “COMPRESS” on page 553.

    Query Banding

    SQL Data Definition Language.

    RADIX command

    “RADIX” on page 579.

    RESETBLCTSKCNT command

    “RESETBLCTSKCNT” on page 580.

    TABLEID command

    “TABLEID” on page 619.