On Thursday 25th April 2019, just two days ago, the Elastic team held the Elastic Stack 7.0 Live (Virtual) Event, in which they explained and showcased several of the features in the latest version of Elasticsearch and its accompanying tools that were released on 10th April.
A recording is available at the link above, and I highly recommend watching it. However, I am writing this summary for the sake of those who might want to quickly check out the highlights without spending close to two hours watching the recording, or for those who want to quickly locate some of the relevant information (video isn’t a great medium to search for info).
“This version of the Elastic Stack looks very different from our early releases. It’s […] a much more mature product. We’ve had… 7 years now to learn and grow. But really we’re still focusing on the same 3 principles that have made Elastic popular from the beginning: speed, scale and relevance.”— Clint Gormley, Stack Team Lead
The Elastic team has invested a lot of work into making Elasticsearch easy to scale, in such a way that it works the same on a laptop and in a data centre with hundreds of nodes with minimal configuration. However, the harsh realities of distributed systems (disk corruptions, split brains, shard inconsistencies etc) make this a very hard problem to solve, and the team has over the years added incremental changes to improve the product’s resiliency.
It is this work that has led to cross-cluster replication (released in 6.5), the removal of the minimum master nodes setting (released in 7.0), and will also enable following a stream of changes as they happen in an index.
“Version 7 is the safest, most flexible, easiest to use and scalable version of Elasticsearch that we’ve ever delivered.”— Clint Gormley, Stack Team Lead
Fundamental changes have also been made in the way search itself works. Elasticsearch 7.0 uses an algorithm called Block Max WAND to greatly improve the speed of queries at the cost of not knowing exactly how many documents matched. This is usually a reasonable tradeoff because people usually want to get the top N results, rather than knowing the total hit count.
The raw speedup given by this new algorithm also has implications in terms of relevance of results and usability. Because search is so fast, it is no longer costly to search for stop words, and thus precision and recall can be improved by including them. Work is also ongoing on a search-as-you-type feature that would not be possible without this new level of performance.
Using BKD-trees instead of inverted indices have also resulted in significant speedups, especially in the realm of geo-shapes where accuracy has also improved considerably as a result.
Kibana got a new design, as its role has grown from being used to visualise Elasticsearch data to becoming an all-encompassing tool to manage the Elastic stack.
Also new on the ingest side is something called the Elastic Common Schema, which is a consistent way to map similar data from different data sources (e.g. Apache, IIS, NGINX) into a single structure.
Kibana 7 Design Considerations
Kibana 7 sports a new design as a result of a design-at-scale problem. The number of services offered by Kibana (see the tab drawer to the left) has increased considerably, and this called for a consistent and usable layout that could cater for applications as diverse as maps and logging.
Some of the more superficial (but by no means trivial) work that went into Kibana was related to making it responsive (i.e. it responds nicely when you resize the browser window) and mobile-friendly (which in the words of Dave Snider, Director of Product design, is still “pretty beta”), as well as the dark mode that applies a darker theme throughout the product.
More importantly, however, Kibana 7 wants users to focus on the content (search results, graphs, visualisations etc) rather than the Kibana tooling itself, and that means moving things like the date picker and even Kibana’s own navigation out of the way.
The new design is based on a set of values:
- Accessible to everyone (colour-blindness, screen reader support, tab around without using a mouse, etc)
- Themable (easy to change colours)
- Responsive (works in different screen sizes)
- Playful (make it feel like fun – lively animations and such)
- Well-documented (important for a distributed and open-source company)
This design was achieved by building the Elastic UI Framework, a React and CSS library of all UI controls used to build Kibana. It is open-source and fully documented with demos.
Making Search Faster (and Easier)
The Block Max WAND algorithm makes search significantly faster when we don’t need the total hit count. A demo showing a query involving stop words showed that the search took more than 10 times as long without this optimisation as it did with it.
The Block Max WAND optimisation, enabled by default in Elasticsearch 7.0, can be disabled at any time using the track_total_hits setting if an exact hit count is required. It is also disabled automatically when using aggregations, to which the optimisation cannot be applied. Even with the optimisation enabled, total hits are tracked up to a maximum of 10,000. You can tell whether the hit count is accurate or not by seeing whether the hits.total.relation value is “eq” (which means it’s accurate) or “gte” (which means the actual hit count will be greater than or equal to 10,000).
This ground-breaking enhancement to the way search works is beneficial not only in speeding up queries, but also in enabling new features. In fact, a search-as-you-type feature is under development and is planned for the 7.1 release. Aside from that, feature fields and interval queries are also mentioned in the presentation.
Cluster Resiliency and Scale
Elasticsearch 7 brings with it a new cluster coordination subsystem, which is responsible for the ongoing healthy operation of an Elasticsearch cluster. This has led to the removal of the minimum_master_nodes setting, which could prove very painful pre-7.0. Master elections are also a lot faster (going from at least 3 seconds in pre-7.0 to a few hundred milliseconds in 7.0), and logging is available when things go wrong.
The new cluster coordination system has been verified using formal methods, typically employed in mission-critical systems. Also, upgrading to this new system can be done without downtime.
An important resiliency enhancement in 7.0 is the real-memory circuit breaker. Elasticsearch uses several circuit breakers, designed to push back on requests when under load to avoid out-of-memory errors. The new real-memory circuit breaker allows Elasticsearch to know exactly how much memory will be allocated, making it less likely to break while at the same time using less overhead.
Elasticsearch 7.0 also introduces production-ready cross-cluster replication, allowing changes to indices to be synchronised with remote Elasticsearch clusters. The slide shown above describes some use cases where this is useful.
Geo Gorgeous (i.e. Maps)
The support for geographical applications by Elasticsearch and Kibana has received a considerable boost in version 7. At a basic level:
- geo_points and geo_shapes now fully use BKD-trees
- Ingest nodes can now use the GeoIP processor, and Logstash has a geoip filter plugin
- Kibana gets a Coordinate Map, Region Map, as well as Vega and Maps capabilities
- An Elastic Maps Service is now available
- A new geo_shape type makes geo_shape fields a lot easier to work with
The use of BKD-trees for Geo Shapes significantly reduces the complexity of their representation, and therefore their storage. This results in considerable speed (indexing and querying), space and accuracy improvements, as shown in the slide above (and further in the video).
Elasticsearch 7.0 also introduces the geo_tile aggregation, which (unlike the geo hashes in use so far) conforms to the Web Mercator specification. Grid tiles are thus actually square, and preserve identical aspect ratio at all scales and latitudes.
The rest of the presentation on geo focuses on Kibana Maps, which is beta in 7.0. It is a great tool allowing compisition of maps from multiple data sources, as the demo shows. The rest of the screenshots below are stills from the demo, and each demonstrates a particular functionality.
Summary (of the Summary)
Elastic Stack 7.0 is packed with new features and improvements. The launch event, still available on video and summarised in this article, barely scratches the surface. There is certainly a lot to be excited about.
Some items we’ve touched upon include:
- Kibana has grown and got a redesign.
- Block Max WAND significantly speeds up search (at the cost of total hit count), and paves the way for future features such as search-as-you-type.
- A new cluster coordination subsystem, real-memory circuit breaker, and cross-cluster replication improve cluster resiliency and scale.
- Significant improvements have been made in the geo space, and Kibana Maps is awesome.