How to use Flush Command in MySQL Effectively?

Question

We are facing a problem, our DB instance MySQL 8.0 (Production environment) is continuously showing an alert that number of open tables is equal to table_open_cache value. The number of open tables is increased more than 43,200 in 24 hour observation period which makes total count of open tables equals to 2845063.

Please help me how to reduce this, If I go for Flush tables command with read only or with read lock will it cause any data loss or performance issues. I have to implement this to my production Database, Is it a good practice to use Flush tables manually once a day.

Posted a question regarding MySQL DB instance open tables, need to know how to reduce the same by any method. Is it a good practice to use Flush tables manually once a day.

I am attaching an image for reference:-

image1

Answer 1

Misses/Hits is about 2% -- reasonable.

Apparently that screenshot should be talking about "opened" tables, not "open" tables. Only 4K are currently "open", limited by table_open_cache .

The image shows 43.2K vs 2.8M -- it is unclear what each means. 43.2K/24h is exactly 1 per 2 seconds. This is suspect.

2.8M openings of tables in 24 hours is high, but not necessarily "bad. (It's about the 95th percentile.)

Suggest increasing table_open_cache to 8000. What activity is going on? Perhaps you are opening a connection, performing a single operation (which involves opening one or more tables), then disconnecting? Can you cut back on the rapidity of creating connections?

Please provide SHOW GLOBAL STATUS LIKE 'Connection'; 50 per second is "high".

I await seeing Opened_tables and Uptime fetched at the 'same' time .

No, I don't think FLUSH is the answer.