|23 Oct 2008||#1|
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Follow-up: Windows Desktop Search
The discussion and email about desktop search offered an opportunity for us to have a deeper architectural discussion about engineering Windows 7. There were a number of comments suggesting alternate implementation methods so we thought we’d discuss another approach and the various pros and cons associated with it. It offers a good example of the engineering balance we are striving for with Windows 7. Chris McConnell wrote this follow-up. --Steven (See you at the PDC in a week!)
Thanks for all the great feedback on our first blog post on Windows Desktop Search. I’ve summarized a number of points that have been made and added some comments about the architectural choices we have made and why.
Integration with the File System
As some posters have pointed out, one possible implementation is to integrate indexing with the file system so that updating a file immediately updates the indices. Windows Desktop Search takes a different approach. There are two aspects of file system integration: knowing when a file changes and actually updating the indices before a file is considered “closed” and available. On an NTFS file system, the indexer is notified whenever a file changes. The indexer never scans the NTFS file system except during the initial index. It is on the second point—updating the indices immediately when a file is closed that we made a different choice. Updating immediately has the benefit that a file is not available until it is indexed, but it also comes with a number of potential disadvantages. We chose to decouple indexing from file system operations because it allows for more flexibility while still being almost real-time. Here are some of the benefits we see in the approach we took:
A number of people expressed frustration with the lack of an advanced query UI. Microsoft has many advanced query user-interfaces in many products, but these are generally focused on well-defined query languages (SQL) or on specific domains (like the Advanced Find in Outlook). With Vista we wanted to address the query problem in a manner more familiar to people today—a single edit control. Our implementation supports a rich query language within that edit control. This is the same approach people are familiar with for web searching for both standard and advanced queries.
We had two observations that led to this approach:
A number comments were about substring matches in filenames, which we do not currently support. This is part of the overall discussion about advanced queries. In order to efficiently execute queries, the indexer builds indices that are based on individual words. In Vista we introduced “searching as you type” to our search UI. Under the hood this is implemented as prefix matches on the indexed words. So when you type, ‘foo’, we look for all terms that start with those letters including ‘food’ and ‘football’. Even more interesting if you type ‘foo net’ we will match on items that have the words ‘food’ and ‘network’ in them. (If what you really want is to match the phrase “foo net” then typing those words inside quotes will do that—another example of advanced query syntax) We have focused primarily on searching for terms found in any property, but there is no question that filenames are special. In recognition of that we support suffix queries on filenames. If you type ‘*food’ then we will return files that end in ‘food’ like “GoodFood”. We do this by reversing the filename and then indexing it as a word. For example, the reverse filename of “GoodFood” would be “DooFdooG” which we index as a word. The suffix query ‘*food” is transformed into a prefix query “doof*” over the reverse filename index—clever, no? So we support prefix matches for all properties and suffix matches for filenames, but we do not support substring matches.
Performance and Citizenship
A number of comments focused on improving performance and citizenship—and we definitely agree on this input. We are always striving to make Windows do more with fewer resources. For those who have turned off indexing all together we hope that our continued improvements will make you reconsider. Even if you organize all of your files and don’t find search useful for files, perhaps you will find start menu search, email search or Internet Explorer 8 address bar search useful. We have worked hard at improving performance and citizenship across Windows. Some of this progress is visible in WS4 and soon in Windows 7. We have improved along all of our dimensions including indexing cost, battery life, citizenship, query speed and scrolling speed. We have some tremendous tools that help us track down performance problems. If you want to help, please contact email@example.com and we will tell you how to collect performance traces we can analyze so that we can continue to make improvements.
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