Hi Peter, Thanks a lot for the suggestion.This would be nice if it performs better.
Is the idea to split one request into smaller parts or will "Select+Delete IDs" just perform better? And regarding the latter option - is this possible in one SQL request? So something like DELETE FROM mytable WHERE id IN ( SELECT id FROM mytable WHERE created_at < some_fixed_millis OFFSET 0 ROWS FETCH NEXT 1000 ROWS ONLY ) And then loop through the results via changing OFFSET and ROWS? (Btw: the column created_at is indexed) Or would you recommend doing this as 2 separate statements in Java/JDBC? Or via maybe even just issuing the original DELETE request more frequent? Regards Peter On 06.10.19 03:50, Peter Ondruška wrote: > Peter, try this if it makes a difference: > > 1. Select entries to be deleted, note their primary keys. > 2. Issue delete using keys to be deleted (1.) and use short > transaction batches. > > On Sun, 6 Oct 2019, 01:33 Peter, <tableyourt...@gmail.com > <mailto:tableyourt...@gmail.com>> wrote: > > Hi, > > I have a table "mytable" with columns "id", "created_at" and "json" > (VARCHAR, BIGINT, LONG VARCHAR), where data is coming in like new 200k > entries every hour and I would like to keep only entries of the last 1 > or 2 hours. It is expected behaviour for the user if too old entries > gets lost as it is some kind of a LRU cache. > > The current solution is to delete entries older than 4 hours every 30 > minutes: > > DELETE FROM mytable WHERE created_at < ? > > I'm using this in a prepared statement where ? is "4 hours ago" in > milliseconds (new DateTime().getMillis()). > > This works, but some (not all) INSERT statement get a bigger delay in > the same order (2-5 seconds) that this DELETE takes, which is ugly. > These INSERT statements are executed independently (using different > threads) of the DELETE. > > Is there a better way? Can I somehow avoid locking the unrelated > INSERT > operations? > > What helps a bit is when I make those deletes more frequently than the > delays will get smaller, but then the number of those delayed requests > will increase. > > What also helps a bit (currently have not seen a negative impact) is > increasing the page size for the Derby Network Server: > -Dderby.storage.pageSize=32768 > > Regards > Peter >
