1. 22 May, 2022 1 commit
  2. 20 Apr, 2022 1 commit
    • yoav-steinberg's avatar
      Optimized `hdr_value_at_percentile` (#10606) · 5075e743
      yoav-steinberg authored
      `hdr_value_at_percentile()` is part of the Hdr_Histogram library
      used when generating `latencystats` report. 
      
      There's a pending optimization for this function which greatly
      affects the performance of `info latencystats`.
      https://github.com/HdrHistogram/HdrHistogram_c/pull/107
      
      
      
      This PR:
      1. Upgrades the sources in _deps/hdr_histogram_ to the latest Hdr_Histogram
        version 0.11.5
      2. Applies the referenced optimization.
      3. Adds minor documentation about the hdr_histogram dependency which was
        missing under _deps/README.md_.
      
      benchmark on my machine:
      running: `redis-benchmark -n 100000 info latencystats` on a clean build with no data.
      
      | benchmark | RPS |
      | ---- | ---- |
      | before upgrade to v0.11.05  | 7,681 |
      | before optimization | 12,474 |
      | after optimization | 52,606 |
      Co-authored-by: default avatarfilipe oliveira <filipecosta.90@gmail.com>
      5075e743
  3. 05 Jan, 2022 1 commit
    • filipe oliveira's avatar
      Added INFO LATENCYSTATS section: latency by percentile distribution/latency by... · 5dd15443
      filipe oliveira authored
      
      Added INFO LATENCYSTATS section: latency by percentile distribution/latency by cumulative distribution of latencies (#9462)
      
      # Short description
      
      The Redis extended latency stats track per command latencies and enables:
      - exporting the per-command percentile distribution via the `INFO LATENCYSTATS` command.
        **( percentile distribution is not mergeable between cluster nodes ).**
      - exporting the per-command cumulative latency distributions via the `LATENCY HISTOGRAM` command.
        Using the cumulative distribution of latencies we can merge several stats from different cluster nodes
        to calculate aggregate metrics .
      
      By default, the extended latency monitoring is enabled since the overhead of keeping track of the
      command latency is very small.
       
      If you don't want to track extended latency metrics, you can easily disable it at runtime using the command:
       - `CONFIG SET latency-tracking no`
      
      By default, the exported latency percentiles are the p50, p99, and p999.
      You can alter them at runtime using the command:
      - `CONFIG SET latency-tracking-info-percentiles "0.0 50.0 100.0"`
      
      
      ## Some details:
      - The total size per histogram should sit around 40 KiB. We only allocate those 40KiB when a command
        was called for the first time.
      - With regards to the WRITE overhead As seen below, there is no measurable overhead on the achievable
        ops/sec or full latency spectrum on the client. Including also the measured redis-benchmark for unstable
        vs this branch. 
      - We track from 1 nanosecond to 1 second ( everything above 1 second is considered +Inf )
      
      ## `INFO LATENCYSTATS` exposition format
      
         - Format: `latency_percentiles_usec_<CMDNAME>:p0=XX,p50....` 
      
      ## `LATENCY HISTOGRAM [command ...]` exposition format
      
      Return a cumulative distribution of latencies in the format of a histogram for the specified command names.
      
      The histogram is composed of a map of time buckets:
      - Each representing a latency range, between 1 nanosecond and roughly 1 second.
      - Each bucket covers twice the previous bucket's range.
      - Empty buckets are not printed.
      - Everything above 1 sec is considered +Inf.
      - At max there will be log2(1000000000)=30 buckets
      
      We reply a map for each command in the format:
      `<command name> : { `calls`: <total command calls> , `histogram` : { <bucket 1> : latency , < bucket 2> : latency, ...  } }`
      Co-authored-by: default avatarOran Agra <oran@redislabs.com>
      5dd15443
  4. 25 Aug, 2020 1 commit