Ordered queue?

Question

Hello, could somebody please advice - I need to build some kind of scheduled queue, where records have a time to execute defined in milliseconds. So a key will be a number, which defines a time stamp, and I would like to open cursor and first record will be a record where the key value is minimal, then next record will have value next to minimal and so on. I saw it is possible to do similar things with Sequence, but in my case I can insert one record with key 17, and another record with key 5, and when I open cursor and query for next record - cursor should return record with key 5 - not 7.

Answer 1

Hi,
The short answer is you can use a sequence or a timestamp in a format that you decide works best based on your queries. The keys will be stored in sorted order so that should give you what you want. JE automatically determines the record's proper placement in the database's internal B-Tree using whatever key and data comparison functions that are available to it.
When you create a cursor and traverse it, you can go in sorted order. For more information:
http://www.oracle.com/technology/documentation/berkeley-db/je/GettingStartedGuide/Cursors.html
To see more information about cursor methods such as get(), previous(), please see:
http://www.oracle.com/technology/documentation/berkeley-db/je/java/com/sleepycat/je/Cursor.html
What logical design do you have in mind? If you describe in more detail your logical design, the type queries you have, I will try to help you further.
Ron