Robbin Zhang writes:
> On Sun, 3 Oct 1999 sinisa@stripped wrote:
>
> > HI!
> >
> > It would be easier for you if you would you one instance of MySQL
> > server, do not use any RAM disk, then on start-up create HEAP tables
> > (available with 3.23.xx) and copy disk tables to HEAP tables. Then,
> > all you have to do is run insert/update/delete to both copies of
> > tables, while SELECT's would be run from the HEAP tables.
> >
>
> Any detail on how to do this ? Can you give a few examples or a pointer
> to the doc ? Thanks !
>
> Robbin
Hi Robbin,
CREATE TABLE test TYPE=HEAP SELECT ip,SUM(downloads) as down FROM
log_table GROUP BY ip;
SELECT COUNT(ip),AVG(down) from test;
DROP TABLE test;
Here are 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 do not use all memory. Indexes will only be used
with = and <=> (but are VERY fast). 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
allocated 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. To ensure that you
accidentally don't do anything stupid, you can't create HEAP tables
bigger than max_heap_table_size.
HEAP is the keyword.
Regards,
- Jani
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> > Do take into account the limitations of HEAP tables.
> >
> > Sinisa
> >
> > +----------------------------------------------------------------------+
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> > +----------------------------------------------------------------------+
> >
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