FAQ
Then why not always write segment.delXXXX, where XXXX is
incremented. Each file may be compressed or uncompressed based on
the number of deletions it contains.

It should not matter in high performance "server mode" cases, since
the deletion data for the segment should be in memory anyway, so no
need to read all of the files (during merging). They are only there
for crash recovery situations.

If you are using lucene in the "shared networking" mode, then
performance is probably not a huge concern anyway, so reading the
multiple files when opening the segment is the penalty.

Or the policy can be pluggable and the "shared" can use the old
bitset method.
On Jan 8, 2009, at 12:04 AM, Marvin Humphrey wrote:
On Wed, Jan 07, 2009 at 10:36:01PM -0600, robert engels wrote:
Yes, and I don't think the "worst-case" is correct.

When you go to write that segment, you determine that it is a "large"
segment, but has few deletions (one in this case), it will be written
compressed in probably less than 10 bytes (1 byte header, vlong
start, vint length - you only write the ones...)...
If a segment slowly accumulates deletions over time during
different indexing
sessions, at some point you will cross the threshold where the
deletions file
needs to be written out as an uncompressed bit vector. From then
on, adding a
single additional deletion to the segment during any subsequent
indexing
session triggers what I'm calling "worst-case" behavior: the whole
bit vector
file needs to be rewritten for the sake of a one deletion.

Marvin Humphrey

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postedJan 8, '09 at 12:01a
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