Avoid normalization when searching
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Key: DIRSERVER-800
URL: http://issues.apache.org/jira/browse/DIRSERVER-800
Project: Directory ApacheDS
Issue Type: Improvement
Reporter: Emmanuel Lecharny
Priority: Critical
Fix For: 1.5.0
Ok, this will be an huge improvment, but also a huge modification. Here is the
rational :
- each time we are searching for an entry using an attribute value, we are
walking a B-Tree doing a comparizon between the given value and the stored
value. if we have N values stored in the B-Tree, we will do something like
Log2(N) comparizons.
- Now, we have to be aware that those comparisons must be done against the
normalized value of the attribute, and using the assocaited MatchingRule. For
instance, "Emmanuel", "EMMANUEL" and "emmanuel" are supposed to be the same
value if there type is CommonName, so we must do an case insensitive comparison.
- a first optimization is already implemented : the incoming value is
normalized _before_ the search, so we avoid a systematic normalization of the
incoming attribute
- but we will normalized each values which have been found into the server
- again, an optimization is implemented : a cache is used to store normalized
values, so it happens that sometime, we just get the normalized value from the
cache.
- but this cache has a limited size, and as it is a cache, each time we want to
hit it, a synchronization occurs, which will lead to some concurrent access to
slowdown.
At this point, the question is :
- why don't we store normalized values of attribute instead of simple values?
The initial (not normalized) value is always present in the entry, so there is
no need to keep it into the indexes.
This optimization could have a huge impact if it appears that, under heavy
loads, the cache synchronization leads to delayed access.
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