This is a much stronger hash function than fnv64a and comparably fast
(with super-fast assembly implementation for amd64).
Performance is not critical here anyway.
The old fnv64a is kept for vectors, where collision detection is in
place and the weakness of the hashing doesn't matter that much. I
implemented a vector version with xxhash and found that xxhash is
slower in all cases except very very high cardinality (where it is
only slightly faster). Also, ``xxhash.New`` comes with an allocation
of 80 bytes. Thus, to keep vectors alloc-free, we needed to add a
`sync.Pool`, which would have an additional performance overhead.
Signed-off-by: beorn7 <beorn@grafana.com>
This makes the collisions a bit less likely by XOR'ing descIDs rather
than adding them up for the collectorID.
Signed-off-by: beorn7 <beorn@grafana.com>
Flush is another of the methods that will call WriteHeader if it
hasn't happened yet. Since we want to call observeWriteHeader (if
set), we need to do the WriteHeader call already here, similar to what
we have done in Write and ReadFrom.
This commit also adds comments explaining the above to not tempt
developers to remove the WriteHeader call.
Signed-off-by: beorn7 <beorn@grafana.com>
It is perfectly possible that a normal GC happens just before the
forced one. Thus seeing 2 GCs is fine.
Whenever this test failed, it was because two GCs were seen.
Signed-off-by: beorn7 <bjoern@rabenste.in>
This is really lame as it essentially just uses longer times to
wait. The test is still timing-dependent and thus could still
theoretically fail with unlucky scheduling. However, we are testing
something that _is_ about timing. Turning this all into something not
timing-dependent would be first quite involved and second might defeat
the purpose of testing code that is inherently about timing.
Let's see how this works out in practice.
Signed-off-by: beorn7 <bjoern@rabenste.in>
We stopped advertising binary-wide setting of a label quite a while
ago. This doc comment was missed in the cleanup.
Signed-off-by: beorn7 <bjoern@rabenste.in>
tl;dr: Return previous memstats if reading new ones takes longer than
1s.
See the doc comment of NewGoCollector for details.
Signed-off-by: beorn7 <bjoern@rabenste.in>
The previous `float64(math.MaxUint64 + 1)` is too close to
`float64(math.MaxUint64)` to actually overflow as indended.
The counter code is actually converting forward and backward and
compare the original and twice-converted value. On most platform, this
will create a deviation and thus trigger the expected behavior. By
sheer "luck", one might end up with the same value and thus still use
the uint64 representation. Which is OK within the precision we can
expect. But it breaks the test. With this change, the next
representable floating point value greater than the floating point
value used to represent math.MaxUint64 is used.
Signed-off-by: Bjoern Rabenstein <bjoern@rabenste.in>
This allows us to simplify a bunch of code while still supporting the
last four Go minor versions.
We have also run into minor annoyances a couple of times by now to
keep supporting 1.7 and 1.8.
It's time to pull the plug!
Signed-off-by: Bjoern Rabenstein <bjoern@rabenste.in>
The context package is available since Go 1.7 which is the minimal version
supported by client_golang.
Signed-off-by: Simon Pasquier <spasquie@redhat.com>
beorn7