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From "Hohl, Gerrit" <g.h...@aurenz.de>
Subject Paging performance problem
Date Mon, 04 Jan 2021 14:43:08 GMT
Hello everyone,

we're trying to use OFFSET and LIMIT for paging. But as our tables our growing, we're running
in some performance problems we didn't expect.

Let's say we have the following structure (the table can also have more columns, but for the
sake of simplicity...):

CREATE TABLE data (id INTEGER NOT NULL, create_timestamp TIMESTAMP NOT NULL, PRIMARY(id));
CREATE INDEX data_create_timestamp_key ON data (create_timestamp ASC);

We have around 5m records in it. And now we do the two following queries:

SELECT * FROM data ORDER BY create_timestamp OFFSET 0 ROWS FETCH NEXT 10 ROWS ONLY;
SELECT * FROM data ORDER BY create_timestamp OFFSET 4499990 ROWS FETCH NEXT 10 ROWS ONLY;

While the first query returns right after it was started, the 2nd query takes almost a minute
to complete.
First we thought that Derby might not have used the index for some reasons.
But the runtime statistics showed that it is using it.

We assume that it is due to the fact that the index might be some kind of unbalanced binary
tree.
Is that true? And is there any work-around?

Gruß
Gerrit

P.S.: We still use Apache Derby 10.14.2.0 as we're still tight to Java 8.

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