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+# GitLab Performance Monitoring
+
+GitLab comes with its own application performance measuring system as of GitLab
+8.4, simply called "GitLab Performance Monitoring". GitLab Performance Monitoring is available in both the
+Community and Enterprise editions.
+
+Apart from this introduction, you are advised to read through the following
+documents in order to understand and properly configure GitLab Performance Monitoring:
+
+- [GitLab Configuration](gitlab_configuration.md)
+- [InfluxDB Install/Configuration](influxdb_configuration.md)
+- [InfluxDB Schema](influxdb_schema.md)
+- [Grafana Install/Configuration](grafana_configuration.md)
+
+## Introduction to GitLab Performance Monitoring
+
+GitLab Performance Monitoring makes it possible to measure a wide variety of statistics
+including (but not limited to):
+
+- The time it took to complete a transaction (a web request or Sidekiq job).
+- The time spent in running SQL queries and rendering HAML views.
+- The time spent executing (instrumented) Ruby methods.
+- Ruby object allocations, and retained objects in particular.
+- System statistics such as the process' memory usage and open file descriptors.
+- Ruby garbage collection statistics.
+
+Metrics data is written to [InfluxDB][influxdb] over [UDP][influxdb-udp]. Stored
+data can be visualized using [Grafana][grafana] or any other application that
+supports reading data from InfluxDB. Alternatively data can be queried using the
+InfluxDB CLI.
+
+## Metric Types
+
+Two types of metrics are collected:
+
+1. Transaction specific metrics.
+1. Sampled metrics, collected at a certain interval in a separate thread.
+
+### Transaction Metrics
+
+Transaction metrics are metrics that can be associated with a single
+transaction. This includes statistics such as the transaction duration, timings
+of any executed SQL queries, time spent rendering HAML views, etc. These metrics
+are collected for every Rack request and Sidekiq job processed.
+
+### Sampled Metrics
+
+Sampled metrics are metrics that can't be associated with a single transaction.
+Examples include garbage collection statistics and retained Ruby objects. These
+metrics are collected at a regular interval. This interval is made up out of two
+parts:
+
+1. A user defined interval.
+1. A randomly generated offset added on top of the interval, the same offset
+ can't be used twice in a row.
+
+The actual interval can be anywhere between a half of the defined interval and a
+half above the interval. For example, for a user defined interval of 15 seconds
+the actual interval can be anywhere between 7.5 and 22.5. The interval is
+re-generated for every sampling run instead of being generated once and re-used
+for the duration of the process' lifetime.
+
+[influxdb]: https://influxdata.com/time-series-platform/influxdb/
+[influxdb-udp]: https://docs.influxdata.com/influxdb/v0.9/write_protocols/udp/
+[grafana]: http://grafana.org/