Support (optional) CRC or long hashkey generation for bodies
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Key: JBMAIL-36
URL: http://jira.jboss.com/jira/browse/JBMAIL-36
Project: JBoss Mail
Type: Sub-task
Versions: 1.0-M4
Reporter: Andrew Oliver
Assigned to: Andrew Oliver
Priority: Critical
Fix For: 1.0-M4
The M3 Message Store prevents bodies from being stored multiple times and
allows messages to stream directly to the DB. For large messages a line by
line hash should be calculable and if it matches an existing message (this
optimizes for disk size but costs performance) then the Mailbox entry is
reassigned to the existing mailstore and then the new body is deleted.
Example.
1. Assume that the following is a 64mb stream that comes in (minus headers) in
duplicate for both mails (meaning we're sending the same file):
body line CRC/checksum/whatever
XXXXXXXXX...XXXXXXXXXXXXXXXXXXX 123456
YYYYYYYYY...YYYYYYYYYYYYYYYYYYY 654321
ZZZZZZZZZ...ZZZZZZZZZZZZZZZZZZZ 321654
............................... ......
XXXXXXXXX...XXXXXXXXXXXXXXXXXXX 123456
YYYYYYYYY...YYYYYYYYYYYYYYYYYYY 654321
ZZZZZZZZZ...ZZZZZZZZZZZZZZZZZZZ 321654
cumulative checksum accurate to at least 1/50000000
12341235125132412512
if a "select body_id from bodies where checksum='12341235125132412512'" returns
more than 1 result then the new body is deleted and the mailbox is assigned to
the older of the two.
So the idea above is important, algorythmic and method suggestions are not (I
don't know my posterior from my elbow when it comes to efficient binary
similarity detection -- I'm just pretty sure that's not to be done by direct
matching on content!).
It is important that minor revisions not cause collisions. So the 1/50000000
target for minimum collision should not be taken to mean if you send me a doc,
I edit it and send it back that it drops my edits and that's okay. It means
that for this to be a viable algoyrthm if I upload the text of a speech and you
upload a completely different speech and somehow the checksum comes out just
right....we could have that 1/50,000,000 chance of two very different documents
getting the same check, a minor revision to either should fix it.
It is also important that proper boundries be created (no chance that one time
we include fuzz surrounding the body and another time we don't).
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