Today’s video is a comparison between the output of the db2mtrk command and the db2top Memory screen. It covers current allocations, high watermarks, and maximum allocations for the instance, database, and application groups of memory pools as well as the repeat mode of db2mtrk.

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Today’s video is a demonstration of buffer pool hit ratio in the Bufferpools screen of db2top. To produce a hit ratio of 100%, we query a single row repeatedly to perform logical reads with no corresponding physical reads. To reduce the hit ratio, we query more data than can fit in the buffer pool, resulting in physical reads.

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Today’s video is a demonstration of the regular expressions (regex) feature of db2top. In the video, I apply regular expressions to the Dynamic SQL screen to filter what SQL statements are shown. I demonstrate setting and clearing a regex, simple regular expressions, and POSIX extended regular expression metacharacters:

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Today’s video is a demonstration of the Locks screen of db2top. In the video, I create a lock chain and launch db2top to examine the Application Status, Object Name, Locked By and Lock Count columns for three applications involved in the chain. I then use the Lock Chain screen to visualize the chain:

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For the second video in this video series, we have a demonstration of the db2top Watch feature. It demonstrates capturing a single application’s SQL, capturing complete database structures to a set of files, and capturing all the dynamic SQL in the cache:

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Over the next few db2top-related blog posts, I am planning to post some videos that demonstrate some of the features I wrote about in earlier posts. First up is the Change Columns Order screen and a video to demonstrate how to change the column order and keep it changed for the next time you launch db2top:

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Up to now, we have been looking mostly at db2top as a tool for observing the behavior of your system in real-time, but background mode and recording and playback has shown us that db2top can produce and examine historical data as well. The db2top tool can also be used to perform an analysis on such historical data and present a performance report. This ‘analysis’ feature is the topic of today’s post.

The db2top Analysis feature is invoked only from the command line. I touched upon it once before as one of the sub-options in my post on the -b command line option. It turns out that the analysis sub-option has many sub-options of its own.

You invoke the analysis option by specifying a -A sub-option with the -b (background) command line option. However, analysis can only be performed for a subset of the various background options. This subset is listed in the table below:

A ‘u’ for Utilities and an ‘F’ for Federated also do not result in an error message when used with the -A sub-option, but do not result in any reports.

There is also a sort order for each such report. This sort order is dependent upon the sort setting for the particular screen in db2top as you have it configured in your .db2toprc file. The easiest way to change the sort order is to:

1. Go into db2top in interactive mode (db2top -d <database name>).
2. Go to the screen for which you wish to perform analysis. For example, press the ‘l’ (lowercase ‘L’) key to go to the Sessions screen.
3. Figure out the number of the column by which you wish to sort. The easiest way to do this is to go to the Change Columns Order screen by pressing the ‘c’ key. The column numbers are on the left.


db2top Column Order screen for the Sessions screen

4. Remember the number of your column and exit the Change Columns Order screen by pressing the Enter key.
5. Sort by the column of your choice by pressing the ‘z’ key (for descending) or the ‘Z’ key (for ascending) and, at the prompt, enter the number of the column you chose.


db2top Sessions descending sort

6. Press the ‘w’ key to record your choice in the .db2toprc configuration file.
7. Quit db2top interactive mode by pressing the ‘q’ key.
8. The next time you run background mode with the analysis option, the sort order you recorded in the .db2toprc file will be used for the report.

The following video demonstrates the above steps using the Sessions Performance Report:

For columns that can have both a cumulative value and a delta value, the sort order is also influenced by whether the -k option has been specified. When you specify -k, db2top reports the cumulative value. Otherwise, the delta value of such columns is reported. Since these reports sum the values over the time period for which they are measured, the cumulative value is less appropriate and also leads to empty output in the “Performance report, breakdown by 300 seconds” and “Performance report, breakdown by 0.5 hour” reports.

The -m sub-option determines how many minutes of measurement go into the analysis report and the -s sub-option determines how many samples of measurement go into the analysis report.

Combining all these options together, we get the following output from a database named sample when we set Delta_RowsRead/s as the sort column for the Session screen in the .db2toprc file and then perform an 11-minute analysis with this command: db2top -d sample -b l -A -m 11

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When a monitoring or reporting tool reaches a certain level of sophistication, it needs to be able to report on itself as well. The db2top tool has a large number of configurable options, so it is fortunate that there is a screen that lets us see the present value of each such option. In today’s post, we will look at the Display Settings screen.

You launch the Display Settings screen by holding the Shift key and pressing the ‘O’ key. The Display Settings screen is designed to fit a screen that is at least 80 columns wide and 33 columns high, as shown below:

db2top Display Settings screen

It reports much of the same information that is reported more tersely in the header of each of the main screens and it adds information about whether the platform is big or little endian, the stream file, the stream size, the number of watch entries, the value of the $EDITOR environment variable, and the build date of db2top itself. You must press the Enter key to return the screen you were viewing before you launched the Display settings screen.

When launched from screens that have tables that can be sorted, the Display Settings screen reports two more pieces of information: the sort column (and whether it is ascending or descending) and the interval for the sort. In these cases, the screen size more suited to fit such information is 35 rows or higher.

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The db2top tool, on each of its various screens, presents a subset of the full capabilities of the DB2 snapshot monitor. In this post, we’ll see how you can use the native snapshot feature to gain access to the full snapshot.

On most db2top screens, you can access the full native snapshot by holding the Shift key and pressing the ‘S’ key. Each screen produces a different kind of snapshot with some screens producing more than one and others not producing any at all.

The table below lists the various screens in db2top and the corresponding native snapshot.

Screen	Native snapshots
Database	get snapshot for dbm global
	get snapshot for db on <database name> global
Sessions	get snapshot for all applications global
Details for agent	get snapshot for application agentid <agentid> global
Tablespaces	get snapshot for tablespaces on <database name> global
Bufferpools	get snapshot for bufferpools on <database name> global
Tables	get snapshot for tables on <database name> global
Dynamic SQL	get snapshot for dynamic sql on <database name> global
Locks	get snapshot for locks on <database name> global
Memory pools	N/A
Statements	N/A
Utilities	get snapshot for dbm global
Partitions*	get snapshot for fcm for all dbpartitionnums at dbpartitionnum <partition number>
	get snapshot for database on <database name> at dbpartitionnum <partition number>
HADR	N/A
Federation	N/A
Bottlenecks	get snapshot for all applications global
Skew Detection	N/A

* You are prompted to specify the partition number before the snapshot is taken

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What good is a tool if you can’t customize it to your liking? Fortunately, db2top is quite customizable. In today’s post, we will look at how you can customize the order in which columns are presented for the majority of those screens in db2top that present their information in a table.

If you remember our look at the .db2toprc file, we saw that column order could be specified for many of the screens by listing out a new order for each screen in the .db2toprc file. Of course, you either needed a very good memory or to have db2top open in some other window while you performed this task. As an alternative, you can set these column orders directly in db2top by pressing the ‘c’ key when you are on any of the screens for which column reordering is supported.

When you press the ‘c’ key on, say, the Locks screen, you get a screen like the following:

db2top Change column order screen for Locks screen

To reorder the columns, you simply type the numbers you see in the Pos column in the order you would like the columns to be shown and separate them by commas. For example, if you want to see Application Status before Application Name, you simply type 2,1 and press Enter. All the other columns will maintain their positions.

Column 0 is always the first column. If you list a zero in your comma-separated list, it will simply print the first column a second time.

The “Change columns order” screen is not available for some screens that have tables:

• Partitions
• Memory
• Bottlenecks
• Skew

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