0.9.0 / 2018-10-15

• [CHANGE] Go1.6 is no longer supported.
• [CHANGE] More refinements of the Registry consistency checks: Duplicated
  labels are now detected, but inconsistent label dimensions are now allowed.
  Collisions with the “magic” metric and label names in Summaries and
  Histograms are detected now. #108 #417 #471
• [CHANGE] Changed ProcessCollector constructor. #219
• [CHANGE] Changed Go counter go_memstats_heap_released_bytes_total to gauge
  go_memstats_heap_released_bytes. #229
• [CHANGE] Unexported LabelPairSorter. #453
• [CHANGE] Removed the Untyped metric from direct instrumentation. #340
• [CHANGE] Unexported MetricVec. #319
• [CHANGE] Removed deprecated Set method from Counter #247
• [CHANGE] Removed deprecated RegisterOrGet and MustRegisterOrGet. #247
• [CHANGE] API client: Introduced versioned packages.
• [FEATURE] A Registerer can be wrapped with prefixes and labels. #357
• [FEATURE] “Describe by collect” helper function. #239
• [FEATURE] Added package testutil. #58
• [FEATURE] Timestamp can be explicitly set for const metrics. #187
• [FEATURE] “Unchecked” collectors are possible now without cheating. #47
• [FEATURE] Pushing to the Pushgateway reworked in package push to support
  many new features. (The old functions are still usable but deprecated.) #372
  #341
• [FEATURE] Configurable connection limit for scrapes. #179
• [FEATURE] New HTTP middlewares to instrument http.Handler and
  http.RoundTripper. The old middlewares and the pre-instrumented /metrics
  handler are (strongly) deprecated. #316 #57 #101 #224
• [FEATURE] “Currying” for metric vectors. #320
• [FEATURE] A Summary can be created without quantiles. #118
• [FEATURE] Added a Timer helper type. #231
• [FEATURE] Added a Graphite bridge. #197
• [FEATURE] Help strings are now optional. #460
• [FEATURE] Added process_virtual_memory_max_bytes metric. #438 #440
• [FEATURE] Added go_gc_cpu_fraction and go_threads metrics. #281 #277
• [FEATURE] Added promauto package with auto-registering metrics. #385 #393
• [FEATURE] Add SetToCurrentTime method to Gauge. #259
• [FEATURE] API client: Add AlertManager, Status, and Target methods. #402
• [FEATURE] API client: Add admin methods. #398
• [FEATURE] API client: Support series API. #361
• [FEATURE] API client: Support querying label values.
• [ENHANCEMENT] Smarter creation of goroutines during scraping. Solves memory
  usage spikes in certain situations. #369
• [ENHANCEMENT] Counters are now faster if dealing with integers only. #367
• [ENHANCEMENT] Improved label validation. #274 #335
• [BUGFIX] Creating a const metric with an invalid Desc returns an error. #460
• [BUGFIX] Histogram observations don't race any longer with exposition. #275
• [BUGFIX] Fixed goroutine leaks. #236 #472
• [BUGFIX] Fixed an error message for exponential histogram buckets. #467
• [BUGFIX] Fixed data race writing to the metric map. #401
• [BUGFIX] API client: Decode JSON on a 4xx respons but do not on 204
  responses. #476 #414

0.8.0 / 2016-08-17

• [CHANGE] Registry is doing more consistency checks. This might break
  existing setups that used to export inconsistent metrics.
• [CHANGE] Pushing to Pushgateway moved to package push and changed to allow
  arbitrary grouping.
• [CHANGE] Removed SelfCollector.
• [CHANGE] Removed PanicOnCollectError and EnableCollectChecks methods.
• [CHANGE] Moved packages to the prometheus/common repo: text, model,
  extraction.
• [CHANGE] Deprecated a number of functions.
• [FEATURE] Allow custom registries. Added Registerer and Gatherer
  interfaces.
• [FEATURE] Separated HTTP exposition, allowing custom HTTP handlers (package
  promhttp) and enabling the creation of other exposition mechanisms.
• [FEATURE] MustRegister is variadic now, allowing registration of many
  collectors in one call.
• [FEATURE] Added HTTP API v1 package.
• [ENHANCEMENT] Numerous documentation improvements.
• [ENHANCEMENT] Improved metric sorting.
• [ENHANCEMENT] Inlined fnv64a hashing for improved performance.
• [ENHANCEMENT] Several test improvements.
• [BUGFIX] Handle collisions in MetricVec.

0.7.0 / 2015-07-27

• [CHANGE] Rename ExporterLabelPrefix to ExportedLabelPrefix.
• [BUGFIX] Closed gaps in metric consistency check.
• [BUGFIX] Validate LabelName/LabelSet on JSON unmarshaling.
• [ENHANCEMENT] Document the possibility to create "empty" metrics in
  a metric vector.
• [ENHANCEMENT] Fix and clarify various doc comments and the README.md.
• [ENHANCEMENT] - (Kind of) solve "The Proxy Problem" of http.InstrumentHandler.
• [ENHANCEMENT] Change responseWriterDelegator.written to int64.

0.6.0 / 2015-06-01

• [CHANGE] Rename process_goroutines to go_goroutines.
• [ENHANCEMENT] Validate label names during YAML decoding.
• [ENHANCEMENT] Add LabelName regular expression.
• [BUGFIX] Ensure alignment of struct members for 32-bit systems.

0.5.0 / 2015-05-06

• [BUGFIX] Removed a weakness in the fingerprinting aka signature code.
  This makes fingerprinting slower and more allocation-heavy, but the
  weakness was too severe to be tolerated.
• [CHANGE] As a result of the above, Metric.Fingerprint is now returning
  a different fingerprint. To keep the same fingerprint, the new method
  Metric.FastFingerprint was introduced, which will be used by the
  Prometheus server for storage purposes (implying that a collision
  detection has to be added, too).
• [ENHANCEMENT] The Metric.Equal and Metric.Before do not depend on
  fingerprinting anymore, removing the possibility of an undetected
  fingerprint collision.
• [FEATURE] The Go collector in the exposition library includes garbage
  collection stats.
• [FEATURE] The exposition library allows to create constant "throw-away"
  summaries and histograms.
• [CHANGE] A number of new reserved labels and prefixes.

0.4.0 / 2015-04-08

• [CHANGE] Return NaN when Summaries have no observations yet.
• [BUGFIX] Properly handle Summary decay upon Write().
• [BUGFIX] Fix the documentation link to the consumption library.
• [FEATURE] Allow the metric family injection hook to merge with existing
  metric families.
• [ENHANCEMENT] Removed cgo dependency and conditional compilation of procfs.
• [MAINTENANCE] Adjusted to changes in matttproud/golang_protobuf_extensions.

0.3.2 / 2015-03-11

• [BUGFIX] Fixed the receiver type of COWMetric.Set(). This method is
  only used by the Prometheus server internally.
• [CLEANUP] Added licenses of vendored code left out by godep.

0.3.1 / 2015-03-04

• [ENHANCEMENT] Switched fingerprinting functions from own free list to
  sync.Pool.
• [CHANGE] Makefile uses Go 1.4.2 now (only relevant for examples and tests).

0.3.0 / 2015-03-03

This is the big one that changes fingerprinting. See below.

As long as you build the Prometheus server only with make, nothing
can go wrong, as the client_golang is vendored then. But if you
build from your own sources (with go build), you will compile in
whatever you have checked out in client_golang.

Version 0.12.0 of the Prometheus server will have a guard to not
accidentally run from a storage with the old fingerprinting.

• [CHANGE] Changed the fingerprinting for metrics. THIS WILL INVALIDATE ALL
  PERSISTED FINGERPRINTS. IF YOU COMPILE THE PROMETHEUS SERVER WITH THIS
  VERSION, YOU HAVE TO WIPE THE PREVIOUSLY CREATED STORAGE.
• [CHANGE] LabelValuesToSignature removed. (Nobody had used it, and it was
  arguably broken.)
• [CHANGE] Vendored dependencies. Those are only used by the Makefile. If
  client_golang is used as a library, the vendoring will stay out of your way.
• [BUGFIX] Remove a weakness in the fingerprinting for metrics. (This made
  the fingerprinting change above necessary.)
• [FEATURE] Added new fingerprinting functions SignatureForLabels and
  SignatureWithoutLabels to be used by the Prometheus server. These functions
  require fewer allocations than the ones currently used by the server.

0.2.0 / 2015-02-23

client_golang 0.2.0 has been released, with the most prominent new feature being server-side histograms. (Documentations will be updated later today to explain usage.)

0.2.0 / 2015-02-23

• [FEATURE] Introduce new Histagram metric type.
• [CHANGE] Ignore process collector errors for now (better error handling
  pending).
• [CHANGE] Use clear error interface for process pidFn.
• [BUGFIX] Fix Go download links for several archs and OSes.
• [ENHANCEMENT] Massively improve Gauge and Counter performance.
• [ENHANCEMENT] Catch illegal label names for summaries in histograms.
• [ENHANCEMENT] Reduce allocations during fingerprinting.
• [ENHANCEMENT] Remove cgo dependency. procfs package will only be included if
  both cgo is available and the build is for an OS with procfs.
• [CLEANUP] Clean up code style issues.
• [CLEANUP] Mark slow test as such and exclude them from travis.
• [CLEANUP] Update protobuf library package name.
• [CLEANUP] Updated vendoring of beorn7/perks.

Early warning: The fingerprinting method has an embarrassing bug (#74), which will be fixed in v0.3.0, but that will obviously invalidate each and every persisted fingerprint. We thought long about a conversion path or allowing to continue with the old fingerprinting method but could not come up with anything feasible. So one more storage wipe is looming...