[hibernate-dev] RE: HSearch: Using sharding and avoiding query on multiple shards
Performance is ALWAYS an issue.
But am I correct in assuming that the performance increase would be
approximately inversely proportional to the number of shards queried?
My point is that the amount of work required to implement this should be
worth what we think the expected gain will be.
John G.
http://thediningphilosopher.blogspot.com
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Today's Topics:
1. HSearch: Using sharding and avoiding query on multiple shards
(Emmanuel Bernard)
2. Re: HSearch: Using sharding and avoiding query on multiple
shards (Sanne Grinovero)
----------------------------------------------------------------------
Message: 1
Date: Wed, 30 Jul 2008 20:36:13 -0400
From: Emmanuel Bernard <emmanuel(a)hibernate.org>
Subject: [hibernate-dev] HSearch: Using sharding and avoiding query on
multiple shards
To: hibernate-dev(a)lists.jboss.org, Aaron Walker
<a.walker(a)base2services.com>
Message-ID: <165DCC1F-BE42-49BA-8537-C8C41F834677(a)hibernate.org>
Content-Type: text/plain; charset="us-ascii"
Today, in Hibernate Search, a query is applied on all shards. We use a
MultiReader to wrap them together.
In some sharding scenario, it makes sense to apply the query on a
single shard or a subset of the shards.
We could add the following API to IndexShardingStrategy
public DirectoryProvider<?>[]
getDirectoryProvidersForQuery(o.a.l.search.Query query);
The query could be analyzed by the sharding strategy to detect boolean
queries on their sharding criteria
//query building
BooleanQuery bQuery = new BooleanQuery();
bQuery.add(regularQuery, Occur.MUST);
bQuery.add( new TermQuery( new Term("distributor.id", "2"),
Occur.MUST ); //only occurs in shard 1
public DirectoryProvider<?>[]
getDirectoryProvidersForQuery(o.a.l.search.Query query) {
if (query instanceof BooleanQuery) {
List<BooleanClause> clauses =
BooleanQuery.class.cast(query).clauses
}
int restrictedShard;
boolean isAllMust = true;
for (BooleanClause clause : clauses) {
if (clause.getOccur() != Occur.MUST) { isAllMust = false; break; }
if ( clause.getQuery() instanceof TermQuery ) {
Term term = TermQuery.class.cast( clause.getQuery() ).getTerm();
if (term.field().equals("distributor.id")) { restrictedShard =
Integer.parse(term.text(); }
}
}
if (isAllMust && restrictedShard != null) return new Provider[]
{ providers[restrictedShard-1] };
else return providers;
}
That's very flexibile but quite hard to implement correctly especially
since the query tree structure might not be trivial
The alternative strategy is to have the following API on
IndexShardingStrategy
public DirectoryProvider<?>[] getDirectoryProvidersForQuery(Object
hint);
and a corresponding fullTextQuery.setShardHint(Object);
A query could "know it targets shard 2 and pass the information to the
strategy through a standard language:
fullTextQuery.setShardHint("Sony");
public DirectoryProvider<?>[] getDirectoryProvidersForQuery(Object
hint) {
if (String.class.isInstance(hint) &&
String.class.cast(hint).equals("Sony")) {
return new Provider[] { providers[2] }
}
else {
return providers;
}
}
WDYT? How useful would that be?
--
Emmanuel Bernard
http://in.relation.to/Bloggers/Emmanuel | http://blog.emmanuelbernard.com
| http://twitter.com/emmanuelbernard
Hibernate Search in Action (http://is.gd/Dl1)