[Xapian-tickets] [Xapian] #737: Fix/improve $filters

[Xapian]

#737: Fix/improve $filters
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 Reporter:  Olly Betts   |             Owner:  Olly Betts
     Type:  enhancement  |            Status:  assigned
 Priority:  normal       |         Milestone:  1.5.0
Component:  Omega        |           Version:
 Severity:  normal       |        Resolution:
 Keywords:               |        Blocked By:
 Blocking:               |  Operating System:  All
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Comment (by Olly Betts):

 Working on this.  My WIP so far addresses the first 3 points (any
 `START`/`END`/`SPAN` filter is now encoded in the same way as date range
 filters from `START.n`, etc are) which gets rid of the  `~~` when these
 aren't used.  Additionally I've shortened the encoding of date range
 filters by a character or two in cases where `SPAN`/`SPAN.n` isn't used.

 > The DEFAULTOP character could be omitted when using the default
 DEFAULTOP.

 We probably could, but it's a single character and omitting it entirely
 seems to complicate things.

 > We could combine some/all of DEFAULTOP, DOCIDORDER and the existing
 SORTREVERSE/SORTAFTER characters - there are currently 2, 3 and 2*2
 states, though more DEFAULTOP values are possible, and about 10+26*2+19=81
 characters which don't need URL encoding, so we could support up to 6
 DEFAULTOP values and encode all of these into one character which
 shouldn't need URL encoding.

 This seems a better approach and potentially saves more.

 > We could encode value slot numbers using something like base64 and save
 bytes when slots > 9 are used (or perhaps encode all the slot numbers
 together such that they'd usually all fit in one byte).

 Not looked into this.

 > Lists of B and N are sorted, so could easily be prefix-compressed -
 reducing the size when there are a lot of either, which is a case where
 keeping the size down matters most.

 Or this.
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Ticket URL: <https://trac.xapian.org/ticket/737#comment:3>
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