ICU folding was enabled yesterday on en, fr, el and he wikis.
It seems to have triggered an issue in elastic that causes many suggester indices to fail:
[2017-01-25 03:27:18,654][DEBUG][action.bulk ] [elastic1044] [enwiktionary_titlesuggest_1485314643][1] failed to execute bulk item (index) index {[enwiktionary_titlesuggest_1485314643][titlesuggest][3057103t], source[{"batch_id":1485314639,"suggest":{"input":["はーい"],"output":"3057103:t:はーい","weight":160700},"suggest-stop":{"input":["はーい"],"output":"3057103:t:はーい","weight":160700}}]} [enwiktionary_titlesuggest_1485314643][[enwiktionary_titlesuggest_1485314643][1]] IndexFailedEngineException[Index failed for [titlesuggest#3057103t]]; nested: IllegalStateException[from state (0) already had transitions added]; at org.elasticsearch.index.engine.InternalEngine.index(InternalEngine.java:462) at org.elasticsearch.index.shard.IndexShard.index(IndexShard.java:601) at org.elasticsearch.index.engine.Engine$Index.execute(Engine.java:836) at org.elasticsearch.action.index.TransportIndexAction.executeIndexRequestOnPrimary(TransportIndexAction.java:237) at org.elasticsearch.action.bulk.TransportShardBulkAction.shardIndexOperation(TransportShardBulkAction.java:327) at org.elasticsearch.action.bulk.TransportShardBulkAction.shardOperationOnPrimary(TransportShardBulkAction.java:120) at org.elasticsearch.action.bulk.TransportShardBulkAction.shardOperationOnPrimary(TransportShardBulkAction.java:68) at org.elasticsearch.action.support.replication.TransportReplicationAction$PrimaryPhase.doRun(TransportReplicationAction.java:639) at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) at org.elasticsearch.action.support.replication.TransportReplicationAction$PrimaryOperationTransportHandler.messageReceived(TransportReplicationAction.java:279) at org.elasticsearch.action.support.replication.TransportReplicationAction$PrimaryOperationTransportHandler.messageReceived(TransportReplicationAction.java:271) at org.elasticsearch.transport.RequestHandlerRegistry.processMessageReceived(RequestHandlerRegistry.java:75) at org.elasticsearch.transport.TransportService$4.doRun(TransportService.java:376) at org.elasticsearch.common.util.concurrent.AbstractRunnable.run(AbstractRunnable.java:37) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at java.lang.Thread.run(Thread.java:745) Caused by: java.lang.IllegalStateException: from state (0) already had transitions added at org.apache.lucene.util.automaton.Automaton.addTransition(Automaton.java:182) at org.apache.lucene.search.suggest.analyzing.XAnalyzingSuggester.replaceSep(XAnalyzingSuggester.java:335) at org.apache.lucene.search.suggest.analyzing.XAnalyzingSuggester.toAutomaton(XAnalyzingSuggester.java:954) at org.apache.lucene.search.suggest.analyzing.XAnalyzingSuggester.toFiniteStrings(XAnalyzingSuggester.java:973) at org.elasticsearch.search.suggest.completion.AnalyzingCompletionLookupProvider.toFiniteStrings(AnalyzingCompletionLookupProvider.java:403) at org.elasticsearch.search.suggest.completion.CompletionTokenStream.incrementToken(CompletionTokenStream.java:63) at org.apache.lucene.index.DefaultIndexingChain$PerField.invert(DefaultIndexingChain.java:634) at org.apache.lucene.index.DefaultIndexingChain.processField(DefaultIndexingChain.java:365) at org.apache.lucene.index.DefaultIndexingChain.processDocument(DefaultIndexingChain.java:321) at org.apache.lucene.index.DocumentsWriterPerThread.updateDocument(DocumentsWriterPerThread.java:234) at org.apache.lucene.index.DocumentsWriter.updateDocument(DocumentsWriter.java:450) at org.apache.lucene.index.IndexWriter.updateDocument(IndexWriter.java:1477) at org.apache.lucene.index.IndexWriter.addDocument(IndexWriter.java:1256) at org.elasticsearch.index.engine.InternalEngine.innerIndex(InternalEngine.java:530) at org.elasticsearch.index.engine.InternalEngine.index(InternalEngine.java:457) ... 16 more
It's unclear yet, but it sounds like a bug in elastic, I'll revert the patch to activate ICU and try to find a workaround.