On Sat, Jun 26, 2010 at 12:05 PM, Owen Shepherd <owen.sheph...@e43.eu>wrote:
> > > SCSU is not that useful for storage compression since fossil already > > uses zlib and it has no other advantages I am aware of. > > Deflate compression is only applied to commits. Deflate has > significant overhead, and is inapplicable to smaller pieces of text > (such as commit strings) which can non-the-less contribute > significantly to size. On the other hand, SCSU performs better than > UTF-8 for the vast majority of real world texts, as has already been > enumerated. > The checkin-comments in Fossil are contained in the manifest artifacts, which are both delta-compressed and deflated prior to storage in the current implementation. Copies of checkin-comments are stored uncompressed in a separate table (the EVENT table) for ease of access during queries such as "timeline". But the amount of text stored there is small. In Fossil's self-hosting repository (with 3409 events) there is 337KB of comment text, or about 2.3% of the total repository space. In the 10-year history of SQLite there are 8664 events with 869KB of text, or 2.2% of the total repository space. In both those examples, the comments are pure ASCII, so SCSU compression would make no difference. But notice that we could store the text as UTF-32 and it would still be less than 10% of the total repository. In contrast, the delta- and deflate-compressed artifacts comprise about 70% and 80% of the repository space for Fossil and SQLite, respectively. The artifact compression is very effective, achieving compression rations of 19:1 for Fossil and 39:1 for SQLite. -- --------------------- D. Richard Hipp d...@sqlite.org
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