When a target is no longer returned from SD stop()
is called. However it may be recreated before the
next scrape interval happens. So we wait to set stalemarkers
until the scrape of the new target would have happened
and been ingested, which is 2 scrape intervals.
If we're shutting down the context will be cancelled,
so return immediately rather than holding things up for potentially
minutes waiting to safely set stalemarkers no newer than now.
If the server starts immediately back up again all is well.
If not, we're missing some stale markers.
In Prometheus 1.x one sample that is out of order
or that has a duplicate timestamp is discarded, and
the rest of the scrape ingestion continues on.
This will now also be true for 2.0.
If metrics_relabel_configs are used to drop metrics, an errSeriesDropped
is returned. This shouldn't be used to return an error at the end of a
append() call.
The automatic GZIP handling of net/http does not preserve
buffers across requests and thus generates a lot of garbage.
We handle GZIP ourselves to circumvent this.t
With this change the scraping caches series references and only
allocates label sets if it has to retrieve a new reference.
pkg/textparse is used to do the conditional parsing and reduce
allocations from 900B/sample to 0 in the general case.
These lines exercise an append in
TestScrapeLoopWrapSampleAppender. Arguably, append shouldn't be tested
there in the first place.
Still it's weird why this fails on Travis:
```
--- FAIL: TestScrapeLoopWrapSampleAppender (0.00s)
scrape_test.go:259: Expected count of 1, got 0
scrape_test.go:290: Expected count of 1, got 0
2017/01/07 22:48:26 http: TLS handshake error from 127.0.0.1:50716: read tcp 127.0.0.1:40265->127.0.0.1:50716: read: connection reset by peer
FAIL
FAIL github.com/prometheus/prometheus/retrieval 3.603s
```
Should anybody ever find out why, please revert this commit accordingly.
