Mysql improve SELECT speed

Question

I\'m currently trying to improve the speed of SELECTS for a MySQL table and would appreciate any suggestions on ways to improve it.

We have over 300 million records

Answer 1

take time to read my answer here: (has similar volumes to yours)

500 millions rows, 15 million row range scan in 0.02 seconds.

MySQL and NoSQL: Help me to choose the right one

then amend your table engine to innodb as follows:

create table tag_date_value
(
tag_id smallint unsigned not null, -- i prefer ints to chars
tag_date datetime not null, -- can we make this date vs datetime ?
value int unsigned not null default 0, -- or whatever datatype you require
primary key (tag_id, tag_date) -- clustered composite PK
)
engine=innodb;

you might consider the following as the primary key instead:

primary key (tag_id, tag_date, value) -- added value save some I/O

but only if value isnt some LARGE varchar type !

query as before:

select
 tag_date, 
 value
from
 tag_date_value
where
 tag_id = 1 and
 tag_date between 'x' and 'y'
order by
 tag_date;

hope this helps :)

EDIT

oh forgot to mention - dont use alter table to change engine type from mysiam to innodb but rather dump the data out into csv files and re-import into a newly created and empty innodb table.

note i'm ordering the data during the export process - clustered indexes are the KEY !

Export

select * into outfile 'tag_dat_value_001.dat' 
fields terminated by '|' optionally enclosed by '"'
lines terminated by '\r\n'
from
 tag_date_value
where
 tag_id between 1 and 50
order by
 tag_id, tag_date;

select * into outfile 'tag_dat_value_002.dat' 
fields terminated by '|' optionally enclosed by '"'
lines terminated by '\r\n'
from
 tag_date_value
where
 tag_id between 51 and 100
order by
 tag_id, tag_date;

-- etc...

Import

import back into the table in correct order !

start transaction;

load data infile 'tag_dat_value_001.dat' 
into table tag_date_value
fields terminated by '|' optionally enclosed by '"'
lines terminated by '\r\n'
(
tag_id,
tag_date,
value
);

commit;

-- etc...