Solr Cache Test

To obtain maximum query performance, Solr stores several different pieces of information using in-memory caches. Result sets, filters and document fields are all cached so that subsequent, similar searches can be handled quickly. Solr maintains various caches and provides users with options to fine tune these caches are per their requirements. The major caches which are used predominently by users are:

Query Cache: It stores the set of document IDs returned by the query, so if next time same query is fired, it doesn't have to go looking but can return the same set of IDs.

Filter Cache: It stores the filters built by Solr in response to filters added to queries.

Document Cache: Stores the document fields requested when showing query results. When Solr is asked to do a search, generally one or more stored fields are requested to be returned with the results. Solr squirrels those document fields away as well, reducing the time required to service subsequent requests for the same document.

Given that there are many caches and tuning options available for each one of them, it is important to monitor the caches to understand if caches are working at optimal performance. For instance if the memory allocated for cache is enough or is it o large that garbage is being accumulated.

eG Enterprise monitors each cache and provides some of the key statistics like number of evictions, hit ratio, number of inserts etc. which can help administrators understand cache effectiveness.

Target of the test : Apache Solr server

Agent deploying the test : An internal/remote agent

Outputs of the test : One set of results for each cache on each of the Solr core in Apache Solr setup.

Configurable parameters for the test

Parameter	Description
Test period	How often should the test be executed
Host	The IP address of the host for which this test is to be configured.
Port	The port at which the target Apache Solr server listens to.
Username & Password	If JMX requires authentication only (but no security), then ensure that the user and password parameters are configured with the credentials of a user with read-write access to JMX.
Confirm Password	Confirm the password by retyping it in this box.
SSL	By default, SSL is disabled for Apache Solr, accordingly SSL flag is set to No by default. If the flag is set to Yes, the eG Agent will start communicating with Apache Solr server HTTPS.
Timeout	By default timeout is 5 secods.
Detailed Diagnosis	To make diagnosis more efficient and accurate, the eG Enterprise embeds an optional detailed diagnostic capability. With this capability, the eG agents can be configured to run detailed, more elaborate tests as and when specific problems are detected. To enable the detailed diagnosis capability of this test for a particular server, choose the On option. To disable the capability, click on the Off option. The option to selectively enable/disable the detailed diagnosis capability will be available only if the following conditions are fulfilled: The eG manager license should allow the detailed diagnosis capability Both the normal and abnormal frequencies configured for the detailed diagnosis measures should not be 0.

Measurements made by the test

Measurement	Description	Measurement Unit	Interpretation
Eviction	Indicates the number of cache evictions for current index searcher.	Number	If the number is going up over the measurements may be an indicator poor cache performance.
RAM memory used	Indicates the actual heap usage of the cache during the last measurement period.	MB	A large size of Cache may not be the ideal as it could accumulate a lot of garbage. This measure along with other metrics can provide better insights for cache tuning.
Hits	Indicates the number of cache hits for the current index searcher during the last measurement	Number	A high number of hits is always preferred, if the number is going down over a series of measurements, you could investigate it further.
Inserts	Indicates the number of inserts in the cache during the last measurement period	Number	A high number of cache inserts could bring down the performance for the time being but eventually the performance will come up and there will be higher number of cache hits.
Lookups	Indicates the number of lookups against the cache.	Number
Size	Indicates the size of cache as configured.	MB	Fine tune this value based on actual cache usage.
Entries count	Indicates the number of cache entries during the last measurement period	Number
Total size	Indicates the size of cache as configured.	Percent	A high value for this measure indicates that the client is using the maximum amount of allocated connections.
Return local stats	Indicates the number of local (from the local shard) response to a "retrieve stats" shard request.	Number
Merge to global stats	Indicates the number of process shard responses that contain partial local stats. Usually this entails combining per-share stats for each term.	Number