Which is the most slow query in MySQL?
This user_match_ratings table contains over 220 million rows (9 gig data or almost 20 gig in indexes). Queries against this table routinely show up in slow.log (threshold > 2 seconds) and is the most frequently logged slow query in the system:
How to search millions of record in SQL Server?
What you need for your query is a full-text index. Most DBMS support it these days. Assuming that your 50 million row table includes duplicates (perhaps that is part of the problem), and assuming SQL Server (the syntax may change but the concept is similar on most RDBMSes), another option is to store domains in a lookup table, e.g.
Is it better to do a full table scan in MySQL?
In fact, even MySQL optimizer currently does not take it into account. For in-memory workload indexes, access might be faster even if 50% of rows are accessed, while for disk IO bound access we might be better off doing a full table scan even if only a few percent or rows are accessed. Let’s do some computations again.
How many rows can a MySQL database handle?
If you’ve been reading enough database-related forums, mailing lists, or blogs you have probably heard complains about MySQL being unable to handle more than 1,000,000 (or select any other number) rows by some of the users.
How to identify performance issues with slow queries?
Performance issues are common problems when administering MySQL databases. Sometimes these problems are, in fact, due to slow queries. In this blog, we’ll deal with slow queries and how to identify these.
Which is the index for the Rating column?
The obvious index for this query is: (rated_user_id, rating). A query that gets data for only one of the million users and needs 17 seconds is doing something wrong: reading from the (rated_user_id, rater_user_id) index and then reading from the table the (hundreds to thousands) values for the rating column, as rating is not in any index.
Why does SQL Server insert into large table take so long?
Recently I have experimented with changing the clustered index of the large table to an identity int column, which has brought the insert down from 3 hours to one hour, but I am still puzzled why this simple query should take so long to run (regardless of the size of the table) CREATE TABLE [dbo].