Update: same with MediaWiki 1.23.6 and then both master versions of CirrusSerach and Elastica

Update: Same with MediaWiki 1.24.0

OK, thank you for the info Chad. How would you suggest to "reindex"?

For reindexing in place, you can still use --reindexAndRemoveOk --indexIdentifier now like the README outlines. Barring that, if you need a full rebuild you have to drop the the index from ES and then run updateSearchIndexConfig.php fresh.

In T75457#818867, @Chad wrote:

We got rid of --startingOver.

No we didn't. Its totally still there:

vagrant@mediawiki-vagrant:~$ php /vagrant/mediawiki/extensions/CirrusSearch/maintenance/updateSearchIndexConfig.php --startOver
content index...
	Fetching Elasticsearch version...1.3.4...ok
	Scanning available plugins...

And its important! I rarely run over `--reindexAndRemoveOk --indexIdentifier``` now but its still useful if you know that your index is totally busted and needs to be rebuilt from scratch whatever the downtime. So, yeah, we won't ever run it in production. But still.

I think I'll need to do another backport release for 1.24 soon anyway. I can grab it then. I'm pretty careful with those backport releases. I make sure the whole test suite passes and I rebuild the index a bunch of times. But I must have missed --startOver the last time I did it. I _think_ those warnings are pretty harmless so you should be able to proceed from there but I'll make sure to squash them soon.

Ok, got it. Thank you Chad and thank you Manybubbles.
CirrusSearch works great also in 1.24.0 so far, just wanted to report the "error".

Thanks again...

Just a short info with MediaWiki 1.24.0. When I use "php updateSearchIndexConfig.php --reindexAndRemoveOk --indexIdentifier now" as Chad suggested the same PHP Warning pops up. See below.

php updateSearchIndexConfig.php --reindexAndRemoveOk --indexIdentifier now    
                       
content index...
        Fetching Elasticsearch version...1.4.1...ok
        Scanning available plugins...
                head
        Setting index identifier...wiki_content_1417707626
        Picking analyzer...german
        Creating index...ok
        Validating analyzers...ok
        Validating mappings...
                Validating mapping...different...corrected
        Validating cache warmers...
PHP Notice:  Undefined index: warmers in /var/www/wiki/extensions/CirrusSearch/includes/Maintenance/CacheWarmers.php on line 95
PHP Warning:  Invalid argument supplied for foreach() in /var/www/wiki/extensions/CirrusSearch/includes/Maintenance/CacheWarmers.php on line 96
PHP Warning:  array_diff_key(): Argument #1 is not an array in /var/www/wiki/extensions/CirrusSearch/includes/Maintenance/CacheWarmers.php on line 47
                Updating Main Page...done
PHP Warning:  array_keys() expects parameter 1 to be array, null given in /var/www/wiki/extensions/CirrusSearch/includes/Maintenance/CacheWarmers.php on line 129
PHP Warning:  Invalid argument supplied for foreach() in /var/www/wiki/extensions/CirrusSearch/includes/Maintenance/CacheWarmers.php on line 129
        Validating aliases...
                Validating content alias...is taken...
                Reindexing...

Change 182297 had a related patch set uploaded (by Chad):
When an index has no warmers it won't return anything

https://gerrit.wikimedia.org/r/182297

Patch-For-Review

Change 182297 merged by jenkins-bot:
When an index has no warmers it won't return anything

https://gerrit.wikimedia.org/r/182297

I can confirm that this is resolved now. I tried the "master" version of CirrusSearch together with MediaWiki 1.24.1.

Thank you again.