Select random ranges and select random points

From Askmonty.org

   * select_random_ranges (select 10 ranges with a delta as parameter)
   * select_random_points (select 100 random points)

Findings:

 select_random_ranges
   * A delta of 100 for the ranges gives 3 - 6%  performance gain
   * A delta of  50 for the ranges gives 3 - 15% performance gain
   * A delta of   5 for the ranges gives up to 70% performance gain
   * A delta of 1 million shows no difference at all.
 
 select_random_points
   * We see up to 150% performance gain fetching index only
   * We see up to  50% performance gain fetching index and data

The absolute numbers are highly RAM depended

   * We see up to 250% performance difference on a 2GB system
   compared to a 4GB system.

MariaDB and MySQL was compiled with

BUILD/compile-amd64-max

MariaDB revision is:

revno: 2742
committer: Igor Babaev <igor@askmonty.org>
branch nick: maria-5.2-keycache
timestamp: Tue 2010-02-16 08:41:11 -0800
message:
 WL#86: Partitioned key cache for MyISAM.
 This is the base patch for the task.

sysbench was run with this parameters:
 --oltp-table-size=20000000 \       # 20 million rows.
 --max-requests=0 \
 --mysql-table-engine=MyISAM \
 --mysql-user=root \
 --mysql-engine-trx=no \
 --myisam-max-rows=50000000 \
 --rand-seed=303

and this variable part of parameters
 --num-threads=$THREADS --test=${TEST_DIR}/${SYSBENCH_TEST}

Configuration used for MariDB:
 --no-defaults \
 --datadir=/mnt/data/sysbench/data \
 --language=./sql/share/english \
 --key_buffer_size=512M \
 --key_cache_partitions=32 \        # Off | 32 | 64
 --max_connections=256 \
 --query_cache_size=0 \
 --query_cache_type=0 \
 --skip-grant-tables \
 --socket=/tmp/mysql.sock \
 --table_open_cache=512 \
 --thread_cache=512 \
 --tmpdir=/mnt/data/sysbench