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From:Michael Widenius Date:May 15 1999 7:58pm
Subject:mySQL 3.23 - question
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>>>>> "Mark" == Mark Papadakis <markp@stripped> writes:

Mark> Hi!
Mark> "One can create in-memory HEAP tables which are extremely fast for lookups.
Mark> "

Mark> Say I have table with over 500.000 rows, can I use this feature to create
Mark> in-me heap tables for
Mark> mem instead of disk lookups thus achieving supreme perfomance and speed? If
Mark> that's so then I
Mark> am going to build a statue for mySQL guys, it is what I 've been dreaming
Mark> for!

Yes; You can fill your memory with HEAP tables if you like :)

From the (recently updated) MySQL manual:

     Here is some things you should consider when you use `HEAP' tables:

        * You should always use specify `MAX_ROWS' in the `CREATE'
          statement to ensure that you accidently use all memory.

        * Indexes will only be used with `=' and `<=>' (but are VERY

        * `HEAP' tables uses a fixed record length format.

        * `HEAP' doesn't support `BLOB/TEXT' columns.

        * `HEAP' doesn't support `AUTO_INCREMENT' columns.

        * `HEAP' doesn't support an index on a `NULL' column.

        * You can have non-unique keys in a `HEAP' table (not that
          normal with hashed tables).

        * `HEAP' tables are shared between all clients (Just like any
          other table).

        * Data for `HEAP' tables are alloced in small blocks. The
          tables are 100 % dynamic (on inserting). No overflow areas
          and no extra key space is needed.  Deleted rows are put in a
          linked list and will be reused when you insert new data into
          the table.

        * To free memory, you should execute `DELETE FROM heap_table' or
          `DROP TABLE heap_table'.

Hope this helps...

mySQL 3.23 - questionMark Papadakis15 May
  • mySQL 3.23 - questionMichael Widenius16 May
  • Re: mySQL 3.23 - questionKenneth Cobler16 May
    • Re: mySQL 3.23 - questionPaul DuBois16 May
    • Re: mySQL 3.23 - questionMichael Widenius22 May