Dear Jeremy, Thank you for your help.
I do have an exact situation you have assume I have. Here is the output of SHOW CREATE TABLE +---------------------------+------------------------------------------- ------------------------------------------------------------------------ ------------------------------------------------------------------------ ------------------------------------------------------------------------ ------------------------------------------------------------------------ ------------------------------------------------------------------------ ---------------------------------------------------+ | Table | Create Table | +---------------------------+------------------------------------------- ------------------------------------------------------------------------ ------------------------------------------------------------------------ ------------------------------------------------------------------------ ------------------------------------------------------------------------ ------------------------------------------------------------------------ ---------------------------------------------------+ | TICKER_HISTORY_PRICE_DATA | CREATE TABLE `TICKER_HISTORY_PRICE_DATA` ( `price_data_ticker` char(8) NOT NULL default '', `price_data_date` date NOT NULL default '0000-00-00', `price_data_open` float default NULL, `price_data_high` float default NULL, `price_data_low` float default NULL, `price_data_close` float default NULL, `price_data_volume` float default NULL, UNIQUE KEY `tidadx` (`price_data_ticker`,`price_data_date`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 | +---------------------------+------------------------------------------- ------------------------------------------------------------------------ ------------------------------------------------------------------------ ------------------------------------------------------------------------ ------------------------------------------------------------------------ ------------------------------------------------------------------------ ---------------------------------------------------+ 1 row in set (0.01 sec) As you can see, Unique KEY is on two first fields, but most of the work, joins & searches, will be done on the second field "price_data_date". Here is my SHOW VARIABLES mysql> show variables; +---------------------------------+------------------------------------- ---------------------------------------------------------------------+ | Variable_name | Value | +---------------------------------+------------------------------------- ---------------------------------------------------------------------+ | back_log | 50 | | basedir | /data/mysql/mysql-standard/reloc/mysql-standard-4.1.10a-sun-solaris2.9-s parc-64bit/ | | binlog_cache_size | 32768 | | bulk_insert_buffer_size | 8388608 | | character_set_client | latin1 | | character_set_connection | latin1 | | character_set_database | latin1 | | character_set_results | latin1 | | character_set_server | latin1 | | character_set_system | utf8 | | character_sets_dir | /data/mysql/mysql-standard/reloc/mysql-standard-4.1.10a-sun-solaris2.9-s parc-64bit/share/mysql/charsets/ | | collation_connection | latin1_swedish_ci | | collation_database | latin1_swedish_ci | | collation_server | latin1_swedish_ci | | concurrent_insert | ON | | connect_timeout | 5 | | datadir | /raid5/mysqldata/ | | date_format | %Y-%m-%d | | datetime_format | %Y-%m-%d %H:%i:%s | | default_week_format | 0 | | delay_key_write | ON | | delayed_insert_limit | 100 | | delayed_insert_timeout | 300 | | delayed_queue_size | 1000 | | expire_logs_days | 0 | | flush | OFF | | flush_time | 0 | | ft_boolean_syntax | + -><()~*:""&| | | ft_max_word_len | 84 | | ft_min_word_len | 4 | | ft_query_expansion_limit | 20 | | ft_stopword_file | (built-in) | | group_concat_max_len | 1024 | | have_archive | YES | | have_bdb | NO | | have_compress | YES | | have_crypt | YES | | have_csv | NO | | have_example_engine | NO | | have_geometry | YES | | have_innodb | YES | | have_isam | NO | | have_ndbcluster | NO | | have_openssl | NO | | have_query_cache | YES | | have_raid | NO | | have_rtree_keys | YES | | have_symlink | YES | | init_connect | | | init_file | | | init_slave | | | innodb_additional_mem_pool_size | 1048576 | | innodb_autoextend_increment | 8 | | innodb_buffer_pool_awe_mem_mb | 0 | | innodb_buffer_pool_size | 8388608 | | innodb_data_file_path | ibdata1:10M:autoextend | | innodb_data_home_dir | | | innodb_fast_shutdown | ON | | innodb_file_io_threads | 4 | | innodb_file_per_table | OFF | | innodb_flush_log_at_trx_commit | 1 | | innodb_flush_method | | | innodb_force_recovery | 0 | | innodb_lock_wait_timeout | 50 | | innodb_locks_unsafe_for_binlog | OFF | | innodb_log_arch_dir | | | innodb_log_archive | OFF | | innodb_log_buffer_size | 1048576 | | innodb_log_file_size | 5242880 | | innodb_log_files_in_group | 2 | | innodb_log_group_home_dir | ./ | | innodb_max_dirty_pages_pct | 90 | | innodb_max_purge_lag | 0 | | innodb_mirrored_log_groups | 1 | | innodb_open_files | 300 | | innodb_table_locks | ON | | innodb_thread_concurrency | 8 | | interactive_timeout | 28800 | | join_buffer_size | 131072 | | key_buffer_size | 402653184 | | key_cache_age_threshold | 300 | | key_cache_block_size | 1024 | | key_cache_division_limit | 100 | | language | /data/mysql/mysql-standard/reloc/mysql-standard-4.1.10a-sun-solaris2.9-s parc-64bit/share/mysql/english/ | | large_files_support | ON | | license | GPL | | local_infile | ON | | locked_in_memory | OFF | | log | OFF | | log_bin | ON | | log_error | | | log_slave_updates | OFF | | log_slow_queries | OFF | | log_update | OFF | | log_warnings | 1 | | long_query_time | 10 | | low_priority_updates | OFF | | lower_case_file_system | OFF | | lower_case_table_names | 0 | | max_allowed_packet | 16776192 | | max_binlog_cache_size | 18446744073709551615 | | max_binlog_size | 1073741824 | | max_connect_errors | 10 | | max_connections | 100 | | max_delayed_threads | 20 | | max_error_count | 64 | | max_heap_table_size | 16777216 | | max_insert_delayed_threads | 20 | | max_join_size | 18446744073709551615 | | max_length_for_sort_data | 1024 | | max_relay_log_size | 0 | | max_seeks_for_key | 18446744073709551615 | | max_sort_length | 1024 | | max_tmp_tables | 32 | | max_user_connections | 0 | | max_write_lock_count | 18446744073709551615 | | myisam_data_pointer_size | 4 | | myisam_max_extra_sort_file_size | 2147483648 | | myisam_max_sort_file_size | 9223372036854775807 | | myisam_recover_options | OFF | | myisam_repair_threads | 1 | | myisam_sort_buffer_size | 67108864 | | net_buffer_length | 16384 | | net_read_timeout | 30 | | net_retry_count | 10 | | net_write_timeout | 60 | | new | OFF | | old_passwords | OFF | | open_files_limit | 1134 | | pid_file | /raid5/mysqldata/SB2000.pid | | port | 3306 | | preload_buffer_size | 32768 | | protocol_version | 10 | | query_alloc_block_size | 8192 | | query_cache_limit | 1048576 | | query_cache_min_res_unit | 4096 | | query_cache_size | 33554432 | | query_cache_type | ON | | query_cache_wlock_invalidate | OFF | | query_prealloc_size | 8192 | | range_alloc_block_size | 2048 | | read_buffer_size | 2093056 | | read_only | OFF | | read_rnd_buffer_size | 8384512 | | relay_log_purge | ON | | rpl_recovery_rank | 0 | | secure_auth | OFF | | server_id | 1 | | skip_external_locking | ON | | skip_networking | OFF | | skip_show_database | OFF | | slave_net_timeout | 3600 | | slow_launch_time | 2 | | socket | /tmp/mysql.sock | | sort_buffer_size | 2097144 | | sql_mode | | | storage_engine | MyISAM | | sync_binlog | 0 | | sync_replication | 0 | | sync_replication_slave_id | 0 | | sync_replication_timeout | 0 | | sync_frm | ON | | system_time_zone | EST | | table_cache | 512 | | table_type | MyISAM | | thread_cache_size | 8 | | thread_concurrency | 8 | | thread_stack | 196608 | | time_format | %H:%i:%s | | time_zone | SYSTEM | | tmp_table_size | 33554432 | | tmpdir | | | transaction_alloc_block_size | 8192 | | transaction_prealloc_size | 4096 | | tx_isolation | REPEATABLE-READ | | version | 4.1.10a-standard-log | | version_comment | MySQL Community Edition - Standard (GPL) | | version_compile_machine | sparc | | version_compile_os | sun-solaris2.9 | | wait_timeout | 28800 | +---------------------------------+------------------------------------- ---------------------------------------------------------------------+ 180 rows in set (0.00 sec) Mikhail Berman -----Original Message----- From: Jeremy Cole [mailto:[EMAIL PROTECTED] Sent: Thursday, November 17, 2005 5:23 PM To: Mikhail Berman Cc: Jasper Bryant-Greene; mysql@lists.mysql.com Subject: Re: A "key" question Hi Mikhail, > I may not have been precise in my question, but the Unique Index in > question is a two fields index, and I was looking to find out wisdom > from the List if there is sense and/or experience in keying > second(left) field on in the Unique Index to speed up a search. If you have a UNIQUE(a, b), then MySQL can use it as an index for (a), or (a, b), but NOT for (b). In this context, it won't help generally to create an index on (a), but it may help to create one on (b) depending on your queries. > I am dealing with 32M rows table, where second field in the Unique > Index is a date field. Unfortunately for my simple "SELECT MAX(Date) > as Latest_Date from THE_TABLE" took 4 minutes and some seconds, so > before I will go and buy bigger server I needed to re-assure myself > that there is no other way. Four minutes to find a MAX(date) is too long for any kind of hardware. It should be much faster. Can you post the output of: * SHOW CREATE TABLE tbl * SHOW VARIABLES FYI: mysql> select max(dep_time) from ontime_all; +---------------------+ | max(dep_time) | +---------------------+ | 2005-05-31 23:59:00 | +---------------------+ 1 row in set (49.76 sec) mysql> select count(*) from ontime_all; +----------+ | count(*) | +----------+ | 33395077 | +----------+ 1 row in set (0.00 sec) Could be a lot faster, even, but these are MERGE tables so it's really 65 tables that are being checked... Regards, Jeremy -- Jeremy Cole MySQL Geek, Yahoo! Inc. Desk: 408 349 5104 -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe: http://lists.mysql.com/[EMAIL PROTECTED]
