SOLR autoCommit vs autoSoftCommit - solr

Question

I'm very confused about and . Here is what I understand
autoSoftCommit - after a autoSoftCommit, if the the SOLR server goes down, the autoSoftCommit documents will be lost.
autoCommit - does a hard commit to the disk and make sure all the autoSoftCommit commits are written to disk and commits any other document.
My following configuration seems to be only with with autoSoftCommit. autoCommit on its own does not seems to be doing any commits. Is there something I am missing ?
<updateHandler class="solr.DirectUpdateHandler2">
<updateLog>
<str name="dir">${solr.ulog.dir:}</str>
</updateLog>
<autoSoftCommit>
<maxDocs>1000</maxDocs>
<maxTime>1200000</maxTime>
</autoSoftCommit>
<autoCommit>
<maxDocs>10000</maxDocs>
<maxTime>120000</maxTime>
<openSearcher>false</openSearcher>
</autoCommit>
</updateHandler>
why is autoCommit working on it's own ?

Answer 1

I think this article will be useful for you. It explains in detail how hard commit and soft commit work, and the tradeoffs that should be taken in account when tuning your system.
I always shudder at this, because any recommendation will be wrong in some cases. My first recommendation would be to not overthink the problem. Some very smart people have tried to make the entire process robust. Try the simple things first and only tweak things as necessary. In particular, look at the size of your transaction logs and adjust your hard commit intervals to keep these “reasonably sized”. Remember that the penalty is mostly the replay-time involved if you restart after a JVM crash. Is 15 seconds tolerable? Why go smaller then?
We’ve seen situations in which the hard commit interval is much shorter than the soft commit interval, see the bulk indexing bit below.
These are places to start.
HEAVY (BULK) INDEXING
The assumption here is that you’re interested in getting lots of data to the index as quickly as possible for search sometime in the future. I’m thinking original loads of a data source etc.
Set your soft commit interval quite long. As in10 minutes. Soft commit is about visibility, and my assumption here is that bulk indexing isn’t about near real time searching so don’t do the extra work of opening any kind of searcher.
Set your hard commit intervals to 15 seconds, openSearcher=false. Again the assumption is that you’re going to be just blasting data at Solr. The worst case here is that you restart your system and have to replay 15 seconds or so of data from your tlog. If your system is bouncing up and down more often than that, fix the reason for that first.
Only after you’ve tried the simple things should you consider refinements, they’re usually only required in unusual circumstances. But they include:
Turning off the tlog completely for the bulk-load operation
Indexing offline with some kind of map-reduce process
Only having a leader per shard, no replicas for the load, then turning on replicas later and letting them do old-style replication to catch up. Note that this is automatic, if the node discovers it is “too far” out of sync with the leader, it initiates an old-style replication. After it has caught up, it’ll get documents as they’re indexed to the leader and keep its own tlog.
etc.
INDEX-HEAVY, QUERY-LIGHT
By this I mean, say, searching log files. This is the case where you have a lot of data coming at the system pretty much all the time. But the query load is quite light, often to troubleshoot or analyze usage.
Set your soft commit interval quite long, up to the maximum latency you can stand for documents to be visible. This could be just a couple of minutes or much longer. Maybe even hours with the capability of issuing a hard commit (openSearcher=true) or soft commit on demand.
Set your hard commit to 15 seconds, openSearcher=false
INDEX-LIGHT, QUERY-LIGHT OR HEAVY
This is a relatively static index that sometimes gets a small burst of indexing. Say every 5-10 minutes (or longer) you do an update
Unless NRT functionality is required, I’d omit soft commits in this situation and do hard commits every 5-10 minutes with openSearcher=true. This is a situation in which, if you’re indexing with a single external indexing process, it might make sense to have the client issue the hard commit.
INDEX-HEAVY, QUERY-HEAVY
This is the Near Real Time (NRT) case, and is really the trickiest of the lot. This one will require experimentation, but here’s where I’d start
Set your soft commit interval to as long as you can stand. Don’t listen to your product manager who says “we need no more than 1 second latency”. Really. Push back hard and see if the user is best served or will even notice. Soft commits and NRT are pretty amazing, but they’re not free.
Set your hard commit interval to 15 seconds.
In my case (index heavy, query heavy), replication master-slave was taking too long time, slowing don the queries to the slave. By increasing the softCommit to 15min and increasing the hardCommit to 1min, the performance improvement was great. Now the replication works with no problems, and the servers can handle much more requests per second.
This is my use case though, I realized I don'r really need the items to be available on the master at real time, since the master is only used for indexing items, and new items are available in the slaves every replication cycle (5min), which is totally ok for my case. you should tune this parameters for your case.

Answer 2

You have openSearcher=false for hard commits. Which means that even though the commit happened, the searcher has not been restarted and cannot see the changes. Try changing that setting and you will not need soft commit.
SoftCommit does reopen the searcher. So if you have both sections, soft commit shows new changes (even if they are not hard-committed) and - as configured - hard commit saves them to disk, but does not change visibility.
This allows to put soft commit to 1 second and have documents show up quickly and have hard commit happen less frequently.

Answer 3

Soft commits are about visibility.
hard commits are about durability.
optimize are about performance.
Soft commits are very fast ,there changes are visible but this changes are not persist (they are only in memory) .So during the crash this changes might be last.
Hard commits changes are persistent to disk.
Optimize is like hard commit but it also merge solr index segments into a single segment for improving performance .But it is very costly.
A commit(hard 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.
auto commit properties we can manage from sorlconfig.xml files.
<autoCommit>
<maxTime>1000</maxTime>
</autoCommit>
<!-- SoftAutoCommit
Perform a 'soft' commit automatically under certain conditions.
This commit avoids ensuring that data is synched to disk.
maxDocs - Maximum number of documents to add since the last
soft commit before automaticly triggering a new soft commit.
maxTime - Maximum amount of time in ms that is allowed to pass
since a document was added before automaticly
triggering a new soft commit.
-->
<autoSoftCommit>
<maxTime>1000</maxTime>
</autoSoftCommit>
References:
https://wiki.apache.org/solr/SolrConfigXml
https://lucene.apache.org/solr/guide/6_6/index.html