Wondering what to do if MySQL TRUNCATE hangs? Our MySQL Support team is here to lend a hand with your queries and issues.

What to do if MySQL TRUNCATE hangs?

Have you been facing trouble when you have a large buffer pool and attempt to drop or truncate a table in MySQL? Worry no more! This article offers you ways to avoid this scenario.

The stall often occurs due to the full scan of the buffer pool carried out by MySQL in order to track down pages that belong to the dropped table. This process involves locking the buffer pool until it is done.

Solutions:

Interestingly truncating a table doesn’t result in a server lockup if our buffer pool is small. Let’s take a look at the different ways to resolve the stalling issue due to large buffer pools:

1. Delete the rows that will be truncated when we truncate the table. Similarly, delete all rows of the table before dropping it.
2. Alternatively, we can use a non-InnoDB storage engine for temporary tables.

   This is done by specifying ENGINE=MyISAM in the CREATE TABLE statement.

   We can also modify the default storage engine to MyISAM with the following configuration option:

   default_tmp_storage_engine = MyISAM

   Our experts would like to point out that TRUNCATE TABLE is DDL, not DML if we use this quick fix.

If the stall period is longer than usual, it may e due to one of the following reasons:

• If the table being dropped or truncated is referred to by foreign keys, the truncate operation has to verify it is not dropping rows that are still being referred to. Hence, locks on other tables can result in a Truncate hang.
• If other queries hold locks on the table that is to be truncated or dropped, the operation has to wait till the competing locks are released.
• The truncate speed will be affected if the new database has Foreign Keys defined referring to that table when the old database did not.

At the end of the day, it is important to remember that truncate speed is affected if the tables are very large in most cases.

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Conclusion

To sum up, our Support Engineers explained the cause behind the holdup when we run a MySQL TRUNCATE command. We also got a look at different ways to resolve this issue.