ES performs well, but we don't use it as a primary data source, and I would advise heavily against using it as one. Things are getting better with the new tran

ES performs well, but we don't use it as a primary data source, and I would advise heavily against using it as one. Things are getting better with the new transaction log, but it's still extremely prone to falling over and to getting consistency issues, and some of the built-in automation can bite you in the ass. Recently we had a node — fortunately an expendable testing box — run out of disk space. ES stopped working, which is fine, but when we restarted it, several of the shards were corrupt, and there was no way to get it working again without dropping the index and recreating it. In another instance, we started getting client downtime because ES had suddenly detected low disk space on one node (its "high watermark" setting is extremely conservative and not based on a statistical regression of when it's going to run out), and had started relocating shards. When it was done, one of the shards were stuck in "RELOCATING" but marked as done; only restarting ES fixed that issue. When we freed up some disk space, it gave us more downtime when it decided to move the shards back. In theory, ES was behaving correctly, but the automation behaviour that kicked in was unnecessary and not desirable in that use case. ES has lots of good parts, but it also has a surprising number of bad parts — ugly stuff you just won't find in Postgres, for example.