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Advanced Compression and Physical I/O



  • damorgan
    damorgan Member Posts: 14,464 Bronze Crown
    Pleasure to make your acquaintance. I, perhaps, paid too much attention to the fact that your rating in the forum is "newbie" and didn't connect the post to the actual author.
  • 819289
    819289 Member Posts: 9
    edited Dec 1, 2010 6:32PM
    I am using 11gR1 on Slolaris platforms. I could not see benefits of compression after using "alter table compress for all operations" command which is supposed to enable compression for 'insert' operations.

    However I can see 50% compression if I use "alter table move compress". Can somebody suggest what may be going on here? Also it works fine if I use Insert /* +Append */ Into ... in compressed table. REDO logs can not be avoided for or application.

    I checked # of blocks for statistics after DBMS_STATS.GATHER_TABLE_STATS.

    For experiment I truncated table, inserted 20000 rows, in uncompressed table took stats and later truncated, compressed (for all operations) and inserted 20000 rows and took stats again.

    There are lot of duplicate values in columns and we do have a CLOB column that does not get populated at all. 1 Block holds around 15 rows (having avg_row_len of 400 bytes) in uncompressed form.

    Do I need some other configuration ?

    Edited by: 816286 on Dec 1, 2010 3:22 PM

    Edited by: 816286 on Dec 1, 2010 3:31 PM
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