11g Compression Uncompressed

In 11g, there is compression for everyone.  I am really impressed with the direction of Oracle w.r.t to compression. The main problem with advance compression is that it requires additional options licensing.  Not  a bad deal if you are trying to save on storage costs; just share the savings with Oracle.

This blog  will discuss the key features and implementation of compression. To start with compression is supported at following levels.

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1.Storage

  • OLTP compression for DML (Structured Data)
  • SecureFiles Compression (Unstructured Data)

2. Network

  • Data Guard redo Compression

3.Backup

  • RMAN compression
  • Data pump compression

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OLTP Compression

  • New compression algorithm uses deferred or batched approach
  • Data is inserted as is without compression until  PCTFREE  value is reached.
  • Compression of data starts once PCTFREE threshold is reached
  • Can be enabled at  table, partition or tablespace level
  • No need of decompressing the data during reads
  • Recommended for low update activity tables

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Data guard Compression

  • Redo is compressed as it is transmitted over a network.
  • Helps efficiently utilize network bandwidth when data guard  is across data centers
  • Faster resynchronization of Data guard  during gap resolution.
  • Recommended for low network bandwidth
  • Implemented with  attribute “COMPRESSION”  of initialization parameter LOG_ARCHIVE_DEST_n

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RMAN Compression

  • Supports compression of backups using ZLIB algorithm
  • Faster compression and low CPU utilization compared to default BZIP2 (10g)
  • Low compression ratio  compared to BZIP2
  • Implement  with  CONFIGURE COMPRESSION ALGORITHM  ‘value’ command where value can be HIGH, MEDIUM(ZLIB) and LOW(LZO).

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Data Pump Compression

  • Compression of metadata introduced in 10g
  • Compression of data introduced in 11g.
  • Both are Inline operation
  • Save on storage allocation
  • No need to uncompress before Import
  • Implemented with COMPRESSION attribute, Values supported are ALL,DATA_ONLY,METADATA_ONLY

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