Being one of the developers of ArangoDB, I would like to use the chance to reply to this as well.
I think there have been various issues with the cluster stability 1.5 years ago, and since then we have put great efforts into making the database much more robust and faster. Many man-years have been dedicated to this since 2017.
1.5 years ago we were shipping release 3.1, which is out of service already. Since then, we have released
* ArangoDB 3.2: this release provided the RocksDB storage engine, which improves parallelism and memory management compared to our traditional mostly-memory storage engine
* ArangoDB 3.3: with a new deployment mode (active failover), plus ease-of-use and replication improvements (e.g. cross-datacenter replication)
* ArangoDB 3.4: latest release, for which we put great emphasis on performance improvements, namely for the RocksDB storage engine (which now also is the default engine in ArangoDB)
In all of the above releases we also worked on improving AQL query execution plans, in order to make queries perform faster in both single server and cluster deployments. Working on the query optimizer and query execution plan improvements is obviously a never-ending task, and not only did we achieved a lot here since 2017, but we still have a lot of ideas for further improvements in this area. So there are more improvements to be expected for the following releases.
All that said, I think it is clear now that my intention is to show that things should have improved a lot compared to the situation 1.5 y ago, and that we will always be working hard to make ArangoDB a better product.
I think there have been various issues with the cluster stability 1.5 years ago, and since then we have put great efforts into making the database much more robust and faster. Many man-years have been dedicated to this since 2017.
1.5 years ago we were shipping release 3.1, which is out of service already. Since then, we have released
* ArangoDB 3.2: this release provided the RocksDB storage engine, which improves parallelism and memory management compared to our traditional mostly-memory storage engine * ArangoDB 3.3: with a new deployment mode (active failover), plus ease-of-use and replication improvements (e.g. cross-datacenter replication) * ArangoDB 3.4: latest release, for which we put great emphasis on performance improvements, namely for the RocksDB storage engine (which now also is the default engine in ArangoDB)
In all of the above releases we also worked on improving AQL query execution plans, in order to make queries perform faster in both single server and cluster deployments. Working on the query optimizer and query execution plan improvements is obviously a never-ending task, and not only did we achieved a lot here since 2017, but we still have a lot of ideas for further improvements in this area. So there are more improvements to be expected for the following releases.
All that said, I think it is clear now that my intention is to show that things should have improved a lot compared to the situation 1.5 y ago, and that we will always be working hard to make ArangoDB a better product.