Dennis Gove created SOLR-9152:
---------------------------------
Summary: Change the default of facet.distrib.mco from false to true
Key: SOLR-9152
URL: https://issues.apache.org/jira/browse/SOLR-9152
Project: Solr
Issue Type: Improvement
Reporter: Dennis Gove
Priority: Minor
SOLR-8988 added a new query option facet.distrib.mco which when set to true
would allow the use of facet.mincount=1 in cloud mode. The previous behavior,
and current default, is that facet.mincount=0 when in cloud mode.
h3. What exactly would be changed?
The default of facet.distrib.mco=false would be changed to
facet.distrib.mco=true.
h3. When is this option effective?
>From the documentation,
{code}
/**
* If we are returning facet field counts, are sorting those facets by their
count, and the minimum count to return is > 0,
* then allow the use of facet.mincount = 1 in cloud mode. To enable this use
facet.distrib.mco=true.
*
* i.e. If the following three conditions are met in cloud mode:
facet.sort=count, facet.limit > 0, facet.mincount > 0.
* Then use facet.mincount=1.
*
* Previously and by default facet.mincount will be explicitly set to 0 when in
cloud mode for this condition.
* In SOLR-8599 and SOLR-8988, significant performance increase has been seen
when enabling this optimization.
*
* Note: enabling this flag has no effect when the conditions above are not
met. For those other cases the default behavior is sufficient.
*/
{code}
h3. What is the result of turning this option on?
When facet.distrib.mco=true is used, and the conditions above are met, then
when Solr is sending requests off to the various shards it will include
facet.mincount=1. The result of this is that only terms with a count > 0 will
be considered when processing the request for that shard. This can result in a
significant performance gain when the field has high cardinality and the
matching docset is relatively small because terms with 0 matches will not be
considered.
As shown in SOLR-8988, the runtime of a single query was reduced from 20
seconds to less than 1 second.
h3. Can this change result in worse performance?
The current thinking is no, worse performance won't be experienced even under
non-optimal scenarios. From the comments in SOLR-8988,
{quote}
Consider you asked for up to 10 terms from shardA with mincount=1 but you
received only 5 terms back. In this case you know, definitively, that a term
seen in the response from shardB but not in the response from shardA could have
at most a count of 0 in shardA. If it had any other count in shardA then it
would have been returned in the response from shardA.
Also, if you asked for up to 10 terms from shardA with mincount=1 and you get
back a response with 10 terms having a count >= 1 then the response is
identical to the one you'd have received if mincount=0.
Because of this, there isn't a scenario where the response would result in more
work than would have been required if mincount=0. For this reason, the decrease
in required work when mincount=1 is *always* either a moot point or a net win.
{quote}
The belief here is that it is safe to change the default of facet.distrib.mco
such that facet.mincount=1 will be used when appropriate. The overall
performance gain can be significant and there is no seen performance cost.
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
---------------------------------------------------------------------
To unsubscribe, e-mail: dev-unsubscr...@lucene.apache.org
For additional commands, e-mail: dev-h...@lucene.apache.org
