3
\$\begingroup\$

What my query is doing:

I have two SQL tables and I want to copy datarows from the one table to the other table. I am doing this for statistics. The source table includes all current member-sessions/logins and with my statistics table I also want to see member-logins of the past. Thus I want to store these data into my bot_sessions_statistics table as well to make sure they are not being updated anymore:

The original query:

INSERT INTO bot_sessions_statistics (member_id, session_token, username, ip_address)
SELECT sessions.member_id, sessions.session_token, sessions.username, sessions.ip_address
FROM bot_sessions AS sessions
LEFT JOIN
(
    SELECT stats.member_id, stats.session_token, stats.username, stats.ip_address
    FROM bot_sessions_statistics as stats
    WHERE date_active >= date(NOW())
) AS stats
ON sessions.member_id = stats.member_id
WHERE latest_renewal >= date(NOW())
AND stats.member_id IS NULL

The performance of the original query:

Query_time: 86.364613  Lock_time: 0.000085 Rows_sent: 0  Rows_examined: 1088312551

The table structures:

Table bot_sessions: bot_sessions table definition

Table bot_sessions_statistics: bot_sessions_statistics table definition

The performance of single queries:

SELECT sessions.member_id, sessions.session_token, sessions.username, sessions.ip_address
FROM bot_sessions AS sessions
WHERE latest_renewal >= date(NOW())

Returns 44.2k rows (Duration: 0.078s / Fetch: 1.607s)

SELECT stats.member_id, stats.session_token, stats.username, stats.ip_address
FROM bot_sessions_statistics as stats
WHERE date_active >= date(NOW())

Returns 23.3k rows (Duration: 0.047s / Fetch 0.920s)

\$\endgroup\$
2
\$\begingroup\$

I have much more experience with SQL Server than with MySQL, but I think that some things very similar:

  1. LEFT JOIN replacement - you are using only member_id from stats inner query. You could just have a direct LEFT JOIN with the bot_sessions_statistics table.

  2. Cluster index candidate - bot_sessions_statistics.date_active looks like it is assigned one time with current time. As time always goes up, it should not create re-orderings. This is particularly useful when fetching multiple columns (index has all the columns) with conditions like >= date(NOW()) (faster seeks).

  3. Possible use of partitioning - I have never used this in MySQL, but this functionality can provide increased performance when seeking data in very large tables. Partitioning by date columns might gain you some performance.

  4. NOT EXISTS instead of LEFT JOIN / IS NULL - generally, it seems that LEFT JOIN with IS NULL is slower that NOT EXISTS.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.