This benchmark currently tests two rather different methods within the
same loop, which makes it hard to see what could be causing a
performance degradation.
Related: #5054.
```
BenchmarkSetAddAttributes/SetAttributes-10 14066331 82.80 ns/op 48 B/op 1 allocs/op
BenchmarkSetAddAttributes/AddAttributes-10 19333711 114.7 ns/op 0 B/op 0 allocs/op
```
Applying attribute limits in `Record` uses value receiver.
But it should add count of dropped attrs.
In this PR I add using of pointer receiver.
Also it's slightly faster with pointer receiver:
```
goos: darwin
goarch: arm64
pkg: go.opentelemetry.io/otel/sdk/log
│ old.txt │ new.txt │
│ sec/op │ sec/op vs base │
SetAddAttributes-10 175.7n ± 3% 159.8n ± 4% -9.08% (p=0.000 n=10)
│ old.txt │ new.txt │
│ B/op │ B/op vs base │
SetAddAttributes-10 48.00 ± 0% 48.00 ± 0% ~ (p=1.000 n=10) ¹
¹ all samples are equal
│ old.txt │ new.txt │
│ allocs/op │ allocs/op vs base │
SetAddAttributes-10 1.000 ± 0% 1.000 ± 0% ~ (p=1.000 n=10) ¹
¹ all samples are equal
```
Fix#5317
According to the
[specification](https://github.com/open-telemetry/opentelemetry-specification/blob/main/specification/logs/sdk.md#logrecord-limits),
there should be a message printed in the SDK's log to indicate to the
user that an attribute was discarded due to such a limit. To prevent
excessive logging, the message must be printed at most once per
`LogRecord` (i.e., not per discarded attribute).
This change centralizes the `Record` dropped field writes and calls a
global logging function. This will at most log once per any `Record`
dropping attributes, meeting the specification requirement.
This does not log once per `Record` when an attribute is dropped. To do
that we would need to maintain state within the `Record` (i.e.
`sync.Mutex` or `sync.Once`). These types cannot be copied, meaning the
`Record` would take on this "no copy" requirement. This seems too
restrictive and with the permissive specification allowing a single log
line, that is the solution added.
---------
Co-authored-by: Robert Pająk <pellared@hotmail.com>
* Replace Record lim methods with DroppedAttributes
* Add changelog entry
* Add TestRecordDroppedAttributes
* Add TestRecordCompactAttr
* Add an indexPool
* Fix gramatical error
* Apply feedback
Reduce indentation level.
* Apply feedback
Comment compactAttr and deduplicate.
* Deduplicate all attributes when added
* Comment why head is not used
* Clarify comments
* Move TestAllocationLimits to new file
Do not run this test when the race detector is on.
* Comment follow-up task
