こんにちは :) On Thu, May 6, 2010 at 9:56 PM, Takayuki Tsunakawa <tsunakawa.ta...@jp.fujitsu.com> wrote: > In use case 1, I don't understand why three versions of each web page > need to be saved, so this is not a helpful example.
Because they want to be able to access multiple versions of the same web page. It's useful for various kinds of algorithms that extract data about the page. > Do you mean that the versioning was invented mainly for the > implementation of Bigtable/HBase and not for the users's sake? Yes. > If the number of maximum versions is set to one when creating tables, is > there any bad effects due to the Bigtable/HBase implementation (e.g. > performance)? No, setting the maximum number of versions to 1 has no negative impact. > If there is no bad impact, I feel it's better for the > default to be one rather than three. And those who want to use > versioning should specify maximum versions when creating tables. Similarly, one could argue "those who don't want to use versioning should set the maximum number of versions to 1 when creating tables". > That reduces the memtable size and disk storage space by storing only one > version. As Kevin said, the premise is that disk space is cheap, so I guess it makes sense to allow multiple versions by default. It can be very helpful when you unintentionally screw up your data. If you have a table in which cells are updated frequently and where you're never interested in anything other than the latest value of each cell, then yes it makes sense to tweak the setting and reduce the maximum number of versions to 1. That's why it's a setting after all :) -- Benoit "tsuna" Sigoure Software Engineer @ www.StumbleUpon.com
