Prepare release 2.20 (#466)

* Prepare release 2.20

Signed-off-by: Yuri Shkuro <[email protected]>

* Fix date

Signed-off-by: Yuri Shkuro <[email protected]>

CHANGELOG.md

@@ -1,11 +1,44 @@
 Changes by Version
 ==================
 
-2.19.1 (unreleased)
+2.20.0 (2019-11-06)
 -------------------
 
-- Nothing yet.
+## New Features
 
+- Allow all in-process spans of a trace to share sampling state (#443) -- Prithvi Raj
+
+  Sampling state is shared between all spans of the trace that are still in memory.
+  This allows implementation of delayed sampling decisions (see below).
+
+- Support delayed sampling decisions (#449) -- Yuri Shkuro
+
+  This is a large structural change to how the samplers work.
+  It allows some samplers to be executed multiple times on different
+  span events (like setting a tag) and make a positive sampling decision
+  later in the span life cycle, or even based on children spans.
+  See [README](./README.md#delayed-sampling) for more details.
+
+  There is a related minor change in behavior of the adaptive (per-operation) sampler,
+  which will no longer re-sample the trace when `span.SetOperation()` is called, i.e. the
+  operation used to make the sampling decision is always the one provided at span creation.
+
+- Add experimental tag matching sampler (#452) -- Yuri Shkuro
+
+  A sampler that can sample a trace based on a certain tag added to the root
+  span or one of its local (in-process) children. The sampler can be used with
+  another experimental `PrioritySampler` that allows multiple samplers to try
+  to make a sampling decision, in a certain priority order.
+
+- [log/zap] Report whether a trace was sampled (#445) -- Abhinav Gupta
+- Allow config.FromEnv() to enrich an existing config object (#436) -- Vineeth Reddy
+
+## Minor patches
+
+- Expose Sampler on Tracer and accept sampler options via Configuration (#460) -- Yuri Shkuro
+- Fix github.com/uber-go/atomic import (#464) -- Yuri Shkuro
+- Add nodejs to crossdock tests (#441) -- Bhavin Gandhi
+- Bump Go compiler version to 1.13 (#453) -- Yuri Shkuro
 
 2.19.0 (2019-09-23)
 -------------------

README.md

@@ -182,6 +182,29 @@ are available:
   1. `RateLimitingSampler` can be used to allow only a certain fixed
      number of traces to be sampled per second.
 
+#### Delayed sampling
+
+Version 2.20 introduced the ability to delay sampling decisions in the life cycle
+of the root span. It involves several features and architectural changes:
+  * **Shared sampling state**: the sampling state is shared across all local
+    (i.e. in-process) spans for a given trace.
+  * **New `SamplerV2` API** allows the sampler to be called at multiple points 
+    in the life cycle of a span:
+    * on span creation
+    * on overwriting span operation name
+    * on setting span tags
+    * on finishing the span
+  * **Final/non-final sampling state**: the new `SamplerV2` API allows the sampler
+    to indicate if the negative sampling decision is final or not (positive sampling
+    decisions are always final). If the decision is not final, the sampler will be
+    called again on further span life cycle events, like setting tags.
+
+These new features are used in the experimental `x.TagMatchingSampler`, which
+can sample a trace based on a certain tag added to the root
+span or one of its local (in-process) children. The sampler can be used with
+another experimental `x.PrioritySampler` that allows multiple samplers to try
+to make a sampling decision, in a certain priority order.
+
 ### Baggage Injection
 
 The OpenTracing spec allows for [baggage][baggage], which are key value pairs that are added

constants.go

@@ -22,7 +22,7 @@ import (
 
 const (
 	// JaegerClientVersion is the version of the client library reported as Span tag.
-	JaegerClientVersion = "Go-2.19.1-dev"
+	JaegerClientVersion = "Go-2.20.0"
 
 	// JaegerClientVersionTagKey is the name of the tag used to report client version.
 	JaegerClientVersionTagKey = "jaeger.version"