TFS Destroy – friend or foe?

While everyone else is blogging about VS 2010 Beta 2, I thought it still may be worth publishing this post that talks about VS 2008 behavior (yes, the old release ;).

One of the features missing in VS 2005 and added in VS 2008 was destroy command; people wanted to get rid of the source control artifacts for good and were unable to do so.

Interestingly, once the command become available it did not become too popular. Come think of it, there are very few cases where one can afford permanently deleting data; after all, source code is most valuable asset any software company has.

But should you decide on using destroy command, there are few important points to keep in mind:

1. Before executing destroy command, you might consider deleting item first. Leaving the item in “quarantine” while deleted for a week or so makes sure nobody uses the item (for example, as part of automated build) will miss it once it is completely gone. And once you are ready to delete it, use /preview switch to double check what files you are going to permanently wiped out

2. If you use destroy, destroy all versions of the item and do not fall for /keephistory option (with or without /stopat flag):

tf destroy $/Project/FolderOldName;C123 /stopat:C156 /keephistory

This option would destroy all (or some as in example above) versions of the item while retaining item’s history. It may be tempting to clean up database from old revisions leaving the history intact; the problem with this usage is that you will not be able to distinguish the revisions deleted when viewing the item’s history. That may lead to the following message when trying to view seemingly valid history:

3. When you execute destroy command, data is not deleted from DB immediately. There is TFSVersionControl Administration job running on TFS Data Tier at scheduled interval that takes care of actual DB purging. You can trigger the job run immediately by using /startcleanup option (or running on SQL Server manually). The job does not take care of cleaning up the warehouse,  it will get updated at warehouse processing scheduled intervals.

On a personal note, my usage of destroy was limited to removing sample & test TFS projects content; I never was able to get enough justification to permanently delete source code, however unused it may be. But your mileage may differ – if you do decide to get into destruction business, there are couple of very useful resources on TFS destroy that are not immediately discoverable through simple search; summary MSDN article and screencast How Do I: Use the TF Destroy Command in Visual Studio Team System 2008? by Richard Hundhausen.

Mirror from my MSDN blog

Work Item customization tidbits: limits of complexity (part 13 of X)

Today I’d like to talk about WIT customization recommendations that will mostly become applicable as your custom Work Item types increase in complexity.

Keep the number of custom fields limited (per TFS server)

One can have a maximum of 1024 fields defined per Team Foundation Server (as every field is represented by a column in SQL Server table, the limitation is that of maximum number of columns per table in SQL Server). That means that if you define new fields (FIELD with the distinct refname attribute) per WIT, you can easily hit this limit after creating a few complex Work Item types. Once the limit is reached, you have to deal with fields maintenance chores (you must delete some of the fields, and to delete them the fields must not be used in any WIT) – not a lot of fun when what you actually tried to achieve was to create new template.

How do you prevent this problem from occurring? Reuse is the key here – remember that even though it may look like you define a new field per Work Item type, fields are (precious) server resource; and even if the same field is used in WI you can specify different behavior for the same field in a different WIT.

Keep the number of rules limited (per Work Item Type)

While you can create multiple rules in WIT, be aware that rules not only affect maintenance complexity (you have to make it work ;), but also affect the performance. So your users may experience less than stellar performance when they create or modify work items. And there is an additional consideration which I will expand upon in the next section, which is called

Keep the number of WI types small (per Team project)

While there is no hard limit on the number of WIT you can create in one Team project, there is technology limitation (SQL Server again!) on how much complexity one may have per project, with numeric complexity index in this case being defined as [Number of rules in WIT] x [Number of WIT in project]. When you have too many WIT (or few of very complex ones) you may hit a limitation of maximum size of columns in SQL Server statement (65,535). It turns out all rules you define in WIT in Team project are eventually represented as part of real complex SQL statement used for WI validation when changing its data (read more techy details in this forum post by Amit Ghosh)

Keep the number of reportable fields small (per TFS server)

If you are not planning on including the fields into SQL Reporting reports, do not mark fields reportable just for the heck of it, since the reportable fields will propagate into TFS data warehouse and that would add extra in terms of performance and space on your TFS data layer.

By the way, to really understand how reporting in TFS works (and how it fits in a big picture) read this excellent post from Vince Blasberg.

In conclusion, I’d like to highlight once more the importance of having test environment whereto you deploy the potential WIT changes prior to production rollout. Consider the situation where you have just deployed new WIT to a Team project, and as a result the users cannot update any WI in the project. Not a happy place to be, is it?

Related posts:
- Work Item Customization: estimate the effort (part 12)
- Work Item Customization: customization and global lists (part 11)
- Work Item Customization: customization process (part 10)
- Work Item Customization: customization tools (part 9)
- Work Item Customization: special fields (part 8)
- Work Item Customization: fields maintenance (part 7)
- Work Item Customization: global lists (part 6)
- Work Item Customization: system fields (part 5)
- Work Item Customization: user interface (part 4)
- Work Item Customization: state transitions (part 3)
- Work Item Customization: conditional field behavior (part 2)
- Work Item Customization: fields definition (part 1)

Mirror on MSDN blog