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Some Implications of Bazaar Size

Third Draft. Aug 11, 1998
Copyright 1997-1998, Forrest J. Cavalier, III Mib Software
All rights reserved. Comments welcome!

2.1 Factors affecting defect "installation"

A defect remains hidden until it is installed and that code used.

"Installation Erosion"
Over the product development lifetime, the number sites where certain code is installed is generally a decreasing percentage of total sites.

After a product stabilizes at a some level of installed sites (determined by market share with respect to other products, market growth, etc) there are tendencies which will fragment or "erode" the effective working size, even if market share for all versions of the product is maintained (or even grows!)

Raymond briefly mentions this "erosion" effect due to what I term "upgrade resistance" and "feature saturation", but does not discuss its implications.
Actually, as I revise in late May 1997 the list is beginning to lose members for an interesting reason. Several people have asked me to unsubscribe them because fetchmail is working so well for them that they no longer need to see the list traffic! Perhaps this is part of the normal life-cycle of a mature bazaar-style project.

Large, popular bazaars are not immune to the effects of erosion. For example, although the customer base for all versions of Linux is quite large, with each release the customer base for the "current" release erodes. And secondly, additional features are going to have only a subset of the current user base as interested (and testing) stakeholders. Large bazaars will also indicate an attractive market inviting commercial or competition by other bazaars (which is less frequent.)

One implication of this observation is that it is wrong to assume that all code is covered equally by testing for a certain length of calendar time just because your "bazaar is large." Later releases will require a longer calendar time to reach the same level of run-time hours. This will slow progress as the product matures.

Fewer sites upgrading in addition to fewer sites which will be using those new features is a "double whammy" for defect detection..

(There is another way that installation erosion occurs: bazaar fracturing. See 4. Other Factors which erode effective size for a discussion.)

Strategies to maintain effective size:

Next: 2.2 Factors affecting defect "reachability" and "triggering"

Up to: 2. Debugging by testing dramatically lowers effective size
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