> In the normal course of events, how quickly would "dirty"
> pages be posted from memory to disc? Would flat files and TI
> datasets be treated the same way?

> In the event of a system failure, how are "dirty" pages handled,
> if at all?

> We need to understand just how protected we are in a process
> that movesrecords from a primary data base to an archive data
> base.

Leonard,

In "the normal course of events" Transaction Manager XM performs
two postings to disc; your TurboIMAGE (TI) data will be fully
protected after the first posting is completed.

XM maintains data structure in memory, known as the XM Journal,
which is really the memory resident portion of the XM log files
stored on every volume set master. TI transactions that transform
the database (e.g., DBPUT, DBDELETE, etc.) are recorded in the
journal before they are committed to disc. The XM journal file is
posted to XM disc log files when one of the following occurs:

o The XM Journal is full; the journal can store up to 64KB.
o Time expiration -- anything from 0.12 to 1 second.
o Block-on-commit, i.e., a process is waiting for the post to
  occur.
o Too many frozen pages. Pages containing the actual TI data are
  frozen in memory until the XM Journal is posted. This means
  these dirty frozen pages cannot be posted to disc until the
  journal is posted.

YMMV as to when XM Journal post is performed and your TI data is
protected. I believe the maximum wait would be 1 second. As long
as this XM Journal post takes place, XM will be able to post the
dirty pages to disc even after a soft system failure (i.e., a
failure in which you don't loose a disc).

Dirty pages get posted back to disc during a XM checkpoint that
occurs when:

(i) the system or user XM log files on disc are half full, or
(ii) the volume set is closed, or
(iii) system is shutdown with a CNTRL-A.

Since MPE/iX 6.5 the size of these both these XM log files became
user configurable, so once again YMMV as to when a checkpoint will
occur. Remember, that this posting of dirty pages, while
comforting, is NOT required for complete TI transaction protection.

Now, what about flat files? In the normal course of events they
are NOT protected by XM. You can protect these files by attaching
them to the serial write queue using the FSETMODE (bit 15)
intrinsic.

Hope this helps, and thank you for showing me that the stuff I
used to teach in the MPE/iX Performance and Tuning course is still
useful :-)

Take care,
frank

======================================================
Frank Alden Smith           HP MPE/iX Certified Professional
Alden Research, Inc.            Instructor -- Consultant
3617 Ligon Road
Ellicott City MD  21042

Phone: (410) 750-2101

"All knowing is doing" -- Humberto Maturana (biologist and teacher)
======================================================

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