Knut Anders Hatlen wrote:
David Goulden <[email protected]> writes:
For these tables we don't use ORDER BY, so hopefully the bug you mentioned
won't affect us. Out of curiosity, is there any advantage to doing a hard
upgrade? Except for the CLOB performance issue, we're quite happy with
version 10.4.
Hi David,
Off the top of my head, I think the advantages you'll get from a hard
upgrade 10.4 -> 10.5 are faster length calculation for CLOBs and one new
system procedure (SYSCS_UTIL.SYSCS_UPDATE_STATISTICS).
Again, this is mostly correct.
For existing CLOBs you won't get the faster length calculation, even if
you do a hard upgrade. CLOBs inserted into a 10.5 database using the
JDBC methods that take a length argument will benefit. If you use the
"length less" JDBC overrides, than you're back to the 10.4 situation
when it comes to the improved length calculation.
Now, we don't really have a good way to upgrade the format of existing
CLOBs yet. One possibility is to run this query:
UPDATE myTable SET clobValue = clobValue || '' [WHERE
length(clobValue) < someThreshold]
This will upgrade the format by concatenating the existing CLOB with the
empty string. However, the concatenation will materialize the CLOB, so
if you have large CLOBs you need to have a lot of memory in the server
(2 GB++).
I have been looking into using a function that just returns the same
CLOB passed in to it, but Derby doesn't support this yet. The advantage
of that approach is that the CLOB hopefully won't be materialized. The
implementation of this functionality has been started under DERBY-4066.
Regards,
--
Kristian
