| From: BROKE::BITHER "Please reply to [email protected]" 26-FEB-1997 08:09:53.66
To: MEMORMAN
CC: BITHER
Subj: Revised new stars article of the one I just sent - sorry, Diane
Hi Mary,
I just revised this right after I sent it to you. Please ignore the other
one!
Thanks! Diane
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TITLE: Questions and Answers About TDC*.DAT Files
PRODUCT: Rdb Transparent Gateway for DB2 3.*, 7.*
OP/SYS: OpenVMS VAX, OpenVMS AXP
Digital UNIX AXP
SOURCE: Oracle Worldwide Customer Support
QUESTION:
What are the TDC*.DAT files sometimes seen generated in SYS$SCRATCH when using
Rdb Transparent Gateway for DB2 (RTG/DB2)?
ANSWER:
TDC_some_number.DAT files created in SYS$SCRATCH are Temporary Data Cache
files. These files get created when read only dbkeys are selected (the default
dbkey mode for RTG/DB2.) If using primary keys as dbkeys or user-designated
dbkeys, then these files do not get created. In this case the gateway sends
dbkey requests down to the underlying database. This is the recommended
solution for eliminating TDC file creation.
You typically see these files in sys$scratch when cursors are being used.
On UNIX platforms these files are placed in /usr/tmp.
Refer to Chapter 11 of the Product Family User's Guide for more
information on Database Keys.
QUESTION:
For read only cursors, is there a TDC file created for each cursor? Or just
one file for the life of the session?
ANSWER:
A true "read only" cursor would probably NOT request dbkeys so would
not generate TDC files. However, an application that fetches dbkeys
can use a read-only cursor and this will generate TDC files. More likely
an application has declared a cursor without explicitly calling it
a read-only cursor. Therefore it is handled as a read-write cursor,
meaning that dbkeys will be fetched. If the dbkey mode is "read-only
dbkeys" (not related to read-only cursors) then TDC files may appear.
If SQL Services is involved, SQL Services internally uses cursors
so all requests through SQL Services fetch dbkeys and will potentially
create TDC files.
The number of files created depends on several factors. In general
there will be a small number of TDC scratch files (like 1 or 2) for
each attach. Their rate of growth will be a function of whether dbkeys
are attach or transaction scoped. If you are having trouble with
large TDC files, and your application can tolerate it, you might
lessen the problem by using transaction (i.e. NOT attach scoped) dbkeys.
QUESTION:
When are the TDC files deleted? When a transaction terminates, or
when the session terminates or is it dependent on the application?
ANSWER:
For VMS the intention is to delete these files on image rundown. On the UNIX
platform it is on session detach. However, a problem has been found on
the VMS platform in that these files are never actually deleted.
This problem has been reported to engineering and will be fixed in a
future version. The workaround is to delete the files manually.
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