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Prometheus

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Project website: http://prometheus.io/ GitHub: https://github.com/prometheus

Sparse High Resolution Histograms​

Co-authored the sparse high resolution histograms in Prometheus with Björn Rabenstein. This work touches almost all of Prometheus codebase - scraping, TSDB, PromQL, recording and alerting rules, etc.

An entire year's work was opened as a single GitHub PR here. Find the detailed design doc by Björn here, and his another document on PromQL extensions here.

I have given three conference talks on this so far:

Out-of-order Ingestion Support​

A sample (timstamp, value) is considered out-of-order if the timestamp is older than the latest timestamp received for that particular time series. Traditionally, the Prometheus TSDB only accepted in-order samples that are less than one hour old, discarding everything else.

I, along with Jesús Vázquez and Dieter Plaetinck, added support to Prometheus TSDB to accept out-of-order without any limits.

Design Doc, Code, Blog Post, Conference talk

Prometheus Alert-Generator Compliance Specification and Test Suite​

Alert-generator is the component responsible for generating reliable and consistent alerts. I authored the 1.0 specification for the Prometheus Alert-Generator compliance that you can find here. I also authored the test suite to automatically test this specification for any software. You can find it here.

Snapshot of In-Memory Chunks on Shutdown for Faster Restarts​

This work takes a snapshot of in-memory data from TSDB while shutting down to speed-up the restart by skipping the WAL replay. This brought down the restart time of Prometheus by up to 80%!

This was added in PR#7229. You can find detailed explanation in this blog post. I also talked about it in this conference talk.

Memory-Mapping of Head Chunks from Disk​

Instead of storing all the compressed samples (called chunks) in the memory, this work flushes them to the disk and memory-maps them from disk. This brought down the memory usage of Promtheus by upto 50%. This was achieved with the combination of PR#6830 and PR#6679.

You can read more about it in this blog post, and a detailed explanation in this blog post. I also talked about it in this conference talk.

@ Modifier in PromQL​

Based on this design doc, I added the @ modifier for PromQL in PR#8121. It let's you pin any part of PromQL to any timestamp that you want, irrespective of the query time.

Learn more in this blog post.

Subquery Support in PromQL​

With PR#4831, I introduced subqueries of the form

<instant_query> '[' <range> ':' [ <resolution> ] ']' [ offset <duration> ]

in Prometheus. It lets you run a PromQL query inside a PromQL query. You can read more about it in this blog post.

Vertical Compaction and Queries in TSDB​

With PR#370, I added support in Prometheus to handle time-overlapping blocks of data. This enabled backfilling of old data into Prometheus.

Persist for State of Alerts Across Restarts​

This was part of my GSoC 2018 work. PR#4061 added support to carry forward the state of alerts across restarts. Read more about it in my blog post.

Unit Testing of Rules in promtool​

This was part of my GSoC 2018 work. PR#4350 added unit testing of rules in the promtool. Read more about it in my blog post.

Performance and Memory Optimizations​

It's more about the investigation than the final fix.