What is Journaling?

Journaling is a critical IRIS feature and a part of what makes IRIS a reliable database. While journaling is fundamental to IRIS, there are nuances, so I wrote this article to summarize (more briefly than our documentation which has all the details) what you need to know. I realize the irony of saying the 27 minute read is brief.

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InterSystems FAQ rubric

If the system does not stop for 24 hours, old journal files will be deleted at 0:30 according to the "Journal file deletion settings".

A possible cause of journal files remaining that are older than the "Journal file deletion settings" is that there are transactions that remain open.

In that case, you will be able to delete the journal file by searching for processes executing transactions and finalizing the transactions.

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Article
· Nov 24, 2023 4m read
Journal File Indexer

Hi community!

In this article, I'm excited to introduce my latest application, Journal File Indexer. The development of this application is rooted in the portal idea DPI-I-270.

In short, this application lets you load and index a log file in a database.

Why?

If you've ever used the log file search function in the management portal, you may have encountered a timeout error or even a blank page. This problem usually occurs when searching a large journal file. Journal File Indexer solves this problem by considerably increasing the speed of searches once the file has been loaded into the database.

Another problem arises during the restoration process. When searching for global entries in a log file to restore old or new values, the management portal doesn't have this specific functionality. A routine must therefore be coded to achieve this. Journal File Indexer comes to the rescue, incorporating a restore function!

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I'm working for an organisation that is running a very old version of InterSystems Cache (5.016) which runs on AIX . The last two times we have re-booted Cache, we have encountered rollbacks. I've been asked two questions. During the rollback it was "How long is it going to take?" and after the system returned, it was "So what caused it?". My answer to both was "I don't know".

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Hi!

Currently, I'm working on a script using %SYS.Journal API.

My journal files are compressed, following the documentation the compression is zstd.

I tried to unzip a file with zstd tool, ex:

apt-get update
apt-get install zstd

zstd -d 20230806.001z -o 20230806.001

20230806.001z        : 92.03%   (909312 => 836859 bytes, 20230806.001) 

Unfortunately, the unzipped file is invalid:

Write ##class(%SYS.Journal.File).IsValidJournal("/usr/irissys/mgr/journal/20230806.001")

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I have several 1GB journals from a LIVE server that I would like to inspect (eg: check which globals have been updated over the time).

Is there a simple way to view those journals using another IRIS instance ? (eg: local installation).

I have been tempted to put those files directly into the journal folder of my local installation and restart the system, however I am concerned that the transactions they contains will be restored and will corrupt the local database.

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Recently I needed to restore a version of a production class, which was overwritten by compilation and running UpdateProduction. As the correct version was unavailable in the source control, I used journals to restore the data. Journals store a plethora of information about what's happening in the system and are quite a powerful tool. This article explains how to work with journals to extract the data you require.

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In the Windows Ressource Manager I can observe multiple parallel processes coming from cache.exe with read operations to journaling files.

All except one of these processes have the same reads(Byte/s). The processes point to different journal files and constantly read between 200 and 3000 Bytes/s.

The corresponding process via PID in the management portal of Caché shows the process %SYS.Monitor.Control.1. In 3 days of uptime on the server it has run 181.632.583 commands and modified 32.140.642 globals.

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