database - MySQL is slow when delete records in large table -


i have query takes long time run. table around 4 million rows. 

delete table value_was null or value_was <= value_now;

i'm hoping create index (value_was, value_now) like

delete table  id1 in (select id1 table value_was null)  or id2 in (select id2 table value_was <= value_now);

this table doesn't have primary key. has 2 composite keys. , guess cannot use same table in subquery, how improve performance of first query?

thanks suggestion appreciated.

updated: db innodb

due way data stored, internal linked list, innodb tables inherently slow @ huge delete operations. changing storage type myisam should make operation awful lot faster - i've seen 100x improvements in similar situations.


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