Question

So I’ve been struggling to run this query. It takes a really long time.
Its MySQL Innodb. The fields I am using are indexed. Its on a pretty beefy server with around 10gig allocated to the innodb pool config thing.

UPDATE TEMP_account_product p
JOIN products_temp c ON (c.`some_id` = p.`old_someid`)
SET p.`product` = c.id
WHERE p.product IS NULL;

The thing to note here is that both tables contain around 900,000 rows. this line brings back around 800,000 records (WHERE p.product IS NULL;)

I have a feeling I’m kinda screwed here but thought Id try anyway.

Answer 1

I think that possible reasons of slow execution of such type of request can be:

• MOST probable – you have an INDEX(es) on updated field and that request is updating lot of rows – in that case MySQL will need to do a lot of work rebuilding that INDEX(es) during UPDATE. In that case just DROP the INDEX(es) before request, and later recreate it (if needed).
• JOIN is slow (you can check it by select with that JOIN) – i.e. join is done w/o INDEXES. Add indexes in that case.
• slow filtering of WHERE (i.e. MySQL make a full scan to filter), – you can check how fast it is by select with same filter.