具有多个线程的事务和锁定

Question

Hi All following is the problem scenario:

I am using MYSQL (Innodb engine), one of my application(C++/MYSQLCAPI) is doing following operation :

START TRANSACTION

truncate my_table

load Data infile into table my_table.

if both the above command [truncate and load ] are successful then COMMIT

else ROLLBACK

now another application(C++/MYSQLCAPI) which is reading this table in every second by following command.

select * from my_table

ERROR: in this read attempt sometime it gets 0 data , what could be the reason for this ?

Answer 1

You're seeing an empty table since truncate table has an implicit commit . If you need to change the entire table in a transaction you can use delete then insert, or try the rename solution presented in this answer

Answer 2

CREATE TABLE new LIKE real;
load `new` by whatever means
if something went wrong, don't do the next two steps.
RENAME TABLE real TO old, new TO real;
DROP TABLE old;

This avoids the problem you mentioned, plus lots of other problems. In particular, it needs no special transaction handling; the RENAME is atomic and very fast.