Whats the best way to implement this use in my database?

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I have a central database containing millions of IDs. And I have a group of users (50-100 users), all being able to request extraction of IDs from this big database.

Atm what I do is when a user sends a GET request, I SELECT 100 ids then update them with the flag USED and return the 100. The problem is, if I get too many requests at the same time, multiple users will receive the same ids (because I dont lock the db when doing select and then update)

If I lock the database my problem will be solved, but it will also be slower.

What other alternative I have?

Thanks!

phpmyadmin mysql sql database
2 Answers

Look ahead another step... What if a "user" gets 100 rows, then keels over dead. Do you have a way to release those 100 for someone else to work on?

You need an extra table to handle "check out" and "check in". Also, use that table to keep track of the "next" 100 to assign to a user.

When a user checks out the 100, a record of that is stored in the table, together with a timestamp and "who" checked them out. If they don't "check them back in within, say, an hour, then you assign that 100 to another user.

Back on something more mundane... How to pick 100. If there is an auto_increment id with no gaps, then use simple math to chunk up the list. If there are a lot of gaps, then use SELECT id FROM tbl WHERE id > $leftoff ORDER BY id LIMIT 100, 1 to get the end of the next 100.

user_17668310

If each user has their own key, you could pull from the millions of IDs starting from their key*10000. For example, user #9 would first get IDs #90000 to #90099, then #90100 to #90199 next time.

You could set the IDs as "Used" before they get sent back, so one user requesting IDs multiple times will never get duplicates. This needn't lock the database for other users.

If they don't request keys more than 100 times before the database can update, this should avoid collisions. You might need to add logic to allow users who request often not to run out, like by having a pool of IDs that can repopulate their supply, but that depends on particulars that aren't clear from the original question.

user_18168940
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