Near Real Time (NRT) search means that documents are available for search almost immediately after being indexed.
This allows additions and updates to documents to be seen in 'near' real time. Solr does not block updates while a commit is in progress. Nor does it wait for background merges to complete before opening a new search of indexes and returning.
With NRT, you can modify a commit command to be a soft commit, which avoids parts of a standard commit that can be costly. You will still want to do standard commits to ensure that documents are in stable storage, but soft commits let you see a very near real time view of the index in the meantime.
However, pay special attention to cache and autowarm settings as they can have a significant impact on NRT performance.
Commits and Optimizing
A commit operation makes index changes visible to new search requests. A hard commit uses the transaction log to get the id of the latest document changes, and also calls fsync on the index files to ensure they have been flushed to stable storage and no data loss will result from a power failure.
A soft commit is much faster since it only makes index changes visible and does not fsync index files or write a new index descriptor. If the JVM crashes or there is a loss of power, changes that occurred after the last hard commit will be lost. Search collections that have NRT requirements (that want index changes to be quickly visible to searches) will want to soft commit often but hard commit less frequently. A softCommit may be "less expensive" in terms of time, but not free, since it can slow throughput.
An optimize is like a hard commit except that it forces all of the index segments to be merged into a single segment first. Depending on the use, this operation should be performed infrequently (e.g., nightly), if at all, since it involves reading and re-writing the entire index. Segments are normally merged over time anyway (as determined by the merge policy), and optimize just forces these merges to occur immediately.
Soft commit takes uses two parameters: maxDocs and maxTime.
| Parameter | Description |
|---|---|
|
Integer. Defines the number of documents to queue before pushing them to the index. It works in conjunction with the |
|
The number of milliseconds to wait before pushing documents to the index. It works in conjunction with the |
Use maxDocs and maxTime judiciously to fine-tune your commit strategies.
AutoCommits
An autocommit also uses the parameters maxDocs and maxTime. However it’s useful in many strategies to use both a hard autocommit and autosoftcommit to achieve more flexible commits.
A common configuration is to do a hard autocommit every 1-10 minutes and a autosoftcommit every second. With this configuration, new documents will show up within about a second of being added, and if the power goes out, soft commits are lost unless a hard commit has been done.
For example:
<autoSoftCommit>
<maxTime>1000</maxTime>
</autoSoftCommit>It’s better to use maxTime rather than maxDocs to modify an autoSoftCommit, especially when indexing a large number of documents through the commit operation. It’s also better to turn off autoSoftCommit for bulk indexing.
Optional Attributes for commit and optimize
| Parameter | Valid Attributes | Description |
|---|---|---|
|
true, false |
Block until a new searcher is opened and registered as the main query searcher, making the changes visible. Default is true. |
|
true, false |
Perform a soft commit. This will refresh the view of the index faster, but without guarantees that the document is stably stored. Default is false. |
|
true, false |
Valid for |
|
integer |
Valid for |
Example of commit and optimize with optional attributes:
<commit waitSearcher="false"/>
<commit waitSearcher="false" expungeDeletes="true"/>
<optimize waitSearcher="false"/>Passing commit and commitWithin Parameters as Part of the URL
Update handlers can also get commit-related parameters as part of the update URL. This example adds a small test document and causes an explicit commit to happen immediately afterwards:
http://localhost:8983/solr/my_collection/update?stream.body=<add><doc>
<field name="id">testdoc</field></doc></add>&commit=trueAlternately, you may want to use this:
http://localhost:8983/solr/my_collection/update?stream.body=<optimize/>This example causes the index to be optimized down to at most 10 segments, but won’t wait around until it’s done (waitFlush=false):
curl 'http://localhost:8983/solr/my_collection/update?optimize=true&maxSegments=10&waitFlush=false'This example adds a small test document with a commitWithin instruction that tells Solr to make sure the document is committed no later than 10 seconds later (this method is generally preferred over explicit commits):
curl http://localhost:8983/solr/my_collection/update?commitWithin=10000
-H "Content-Type: text/xml" --data-binary '<add><doc><field name="id">testdoc</field></doc></add>'Changing default commitWithin Behavior
The commitWithin settings allow forcing document commits to happen in a defined time period. This is used most frequently with Near Real Time Searching, and for that reason the default is to perform a soft commit. This does not, however, replicate new documents to slave servers in a master/slave environment. If that’s a requirement for your implementation, you can force a hard commit by adding a parameter, as in this example:
<commitWithin>
<softCommit>false</softCommit>
</commitWithin>With this configuration, when you call commitWithin as part of your update message, it will automatically perform a hard commit every time.