Return annotations (warnings and infos) from PromQL queries
This generalizes the warnings we have already used before (but only for problems with remote read) as "annotations".
Annotations can be warnings or infos (the latter could be false positives). We do not treat them different in the API for now and return them all as "warnings". It would be easy to distinguish them and return infos separately, should that appear useful in the future.
The new annotations are then used to create a lot of warnings or infos during PromQL evaluations. Partially these are things we have wanted for a long time (e.g. inform the user that they have applied `rate` to a metric that doesn't look like a counter), but the new native histograms have created even more needs for those annotations (e.g. if a query tries to aggregate float numbers with histograms).
The annotations added here are not yet complete. A prominent example would be a warning about a range too short for a rate calculation. But such a warnings is more tricky to create with good fidelity and we will tackle it later.
Another TODO is to take annotations into account when evaluating recording rules.
---------
Signed-off-by: Jeanette Tan <jeanette.tan@grafana.com>
Using github.com/klauspost/compress package to replace the current Gzip Handler on the API.
We see significant improvements using this handler over the current one as shown in the benchmark added.
Also:
* move selection of compression from `newCompressedResponseWriter` to `*CompressionHandler.ServeHTTP`.
* renaming `compressedResponseWriter` since it now only does one kind of compression.
Signed-off-by: Alan Protasio <alanprot@gmail.com>
This reverts the removal of type casting due to an error in the
dragonfly integration. The change in the type casting introduced by the
commit causes a type mismatch, resulting in the following errors:
util/runtime/limits_default.go:42:57: cannot use rlimit.Cur (variable of type int64) as type uint64 in argument to limitToString
util/runtime/limits_default.go:42:90: cannot use rlimit.Max (variable of type int64) as type uint64 in argument to limitToString
Reverting this commit to resolve the type mismatch error and maintain compatibility with the dragonfly integration.
Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>
Wiser coders than myself have come to the conclusion that a `switch`
statement is almost always superior to a statement that includes any
`else if`.
The exceptions that I have found in our codebase are just these two:
* The `if else` is followed by an additional statement before the next
condition (separated by a `;`).
* The whole thing is within a `for` loop and `break` statements are
used. In this case, using `switch` would require tagging the `for`
loop, which probably tips the balance.
Why are `switch` statements more readable?
For one, fewer curly braces. But more importantly, the conditions all
have the same alignment, so the whole thing follows the natural flow
of going down a list of conditions. With `else if`, in contrast, all
conditions but the first are "hidden" behind `} else if `, harder to
spot and (for no good reason) presented differently from the first
condition.
I'm sure the aforemention wise coders can list even more reasons.
In any case, I like it so much that I have found myself recommending
it in code reviews. I would like to make it a habit in our code base,
without making it a hard requirement that we would test on the CI. But
for that, there has to be a role model, so this commit eliminates all
`if else` occurrences, unless it is autogenerated code or fits one of
the exceptions above.
Signed-off-by: beorn7 <beorn@grafana.com>
We haven't updated golint-ci in our CI yet, but this commit prepares
for that.
There are a lot of new warnings, and it is mostly because the "revive"
linter got updated. I agree with most of the new warnings, mostly
around not naming unused function parameters (although it is justified
in some cases for documentation purposes – while things like mocks are
a good example where not naming the parameter is clearer).
I'm pretty upset about the "empty block" warning to include `for`
loops. It's such a common pattern to do something in the head of the
`for` loop and then have an empty block. There is still an open issue
about this: https://github.com/mgechev/revive/issues/810 I have
disabled "revive" altogether in files where empty blocks are used
excessively, and I have made the effort to add individual
`// nolint:revive` where empty blocks are used just once or twice.
It's borderline noisy, though, but let's go with it for now.
I should mention that none of the "empty block" warnings for `for`
loop bodies were legitimate.
Signed-off-by: beorn7 <beorn@grafana.com>
In the past, every sample value was a float, so it was fine to call a
variable holding such a float "value" or "sample". With native
histograms, a sample might have a histogram value. And a histogram
value is still a value. Calling a float value just "value" or "sample"
or "V" is therefore misleading. Over the last few commits, I already
renamed many variables, but this cleans up a few more places where the
changes are more invasive.
Note that we do not to attempt naming in the JSON APIs or in the
protobufs. That would be quite a disruption. However, internally, we
can call variables as we want, and we should go with the option of
avoiding misunderstandings.
Signed-off-by: beorn7 <beorn@grafana.com>
In other words: Instead of having a “polymorphous” `Point` that can
either contain a float value or a histogram value, use an `FPoint` for
floats and an `HPoint` for histograms.
This seemingly small change has a _lot_ of repercussions throughout
the codebase.
The idea here is to avoid the increase in size of `Point` arrays that
happened after native histograms had been added.
The higher-level data structures (`Sample`, `Series`, etc.) are still
“polymorphous”. The same idea could be applied to them, but at each
step the trade-offs needed to be evaluated.
The idea with this change is to do the minimum necessary to get back
to pre-histogram performance for functions that do not touch
histograms. Here are comparisons for the `changes` function. The test
data doesn't include histograms yet. Ideally, there would be no change
in the benchmark result at all.
First runtime v2.39 compared to directly prior to this commit:
```
name old time/op new time/op delta
RangeQuery/expr=changes(a_one[1d]),steps=1-16 391µs ± 2% 542µs ± 1% +38.58% (p=0.000 n=9+8)
RangeQuery/expr=changes(a_one[1d]),steps=10-16 452µs ± 2% 617µs ± 2% +36.48% (p=0.000 n=10+10)
RangeQuery/expr=changes(a_one[1d]),steps=100-16 1.12ms ± 1% 1.36ms ± 2% +21.58% (p=0.000 n=8+10)
RangeQuery/expr=changes(a_one[1d]),steps=1000-16 7.83ms ± 1% 8.94ms ± 1% +14.21% (p=0.000 n=10+10)
RangeQuery/expr=changes(a_ten[1d]),steps=1-16 2.98ms ± 0% 3.30ms ± 1% +10.67% (p=0.000 n=9+10)
RangeQuery/expr=changes(a_ten[1d]),steps=10-16 3.66ms ± 1% 4.10ms ± 1% +11.82% (p=0.000 n=10+10)
RangeQuery/expr=changes(a_ten[1d]),steps=100-16 10.5ms ± 0% 11.8ms ± 1% +12.50% (p=0.000 n=8+10)
RangeQuery/expr=changes(a_ten[1d]),steps=1000-16 77.6ms ± 1% 87.4ms ± 1% +12.63% (p=0.000 n=9+9)
RangeQuery/expr=changes(a_hundred[1d]),steps=1-16 30.4ms ± 2% 32.8ms ± 1% +8.01% (p=0.000 n=10+10)
RangeQuery/expr=changes(a_hundred[1d]),steps=10-16 37.1ms ± 2% 40.6ms ± 2% +9.64% (p=0.000 n=10+10)
RangeQuery/expr=changes(a_hundred[1d]),steps=100-16 105ms ± 1% 117ms ± 1% +11.69% (p=0.000 n=10+10)
RangeQuery/expr=changes(a_hundred[1d]),steps=1000-16 783ms ± 3% 876ms ± 1% +11.83% (p=0.000 n=9+10)
```
And then runtime v2.39 compared to after this commit:
```
name old time/op new time/op delta
RangeQuery/expr=changes(a_one[1d]),steps=1-16 391µs ± 2% 547µs ± 1% +39.84% (p=0.000 n=9+8)
RangeQuery/expr=changes(a_one[1d]),steps=10-16 452µs ± 2% 616µs ± 2% +36.15% (p=0.000 n=10+10)
RangeQuery/expr=changes(a_one[1d]),steps=100-16 1.12ms ± 1% 1.26ms ± 1% +12.20% (p=0.000 n=8+10)
RangeQuery/expr=changes(a_one[1d]),steps=1000-16 7.83ms ± 1% 7.95ms ± 1% +1.59% (p=0.000 n=10+8)
RangeQuery/expr=changes(a_ten[1d]),steps=1-16 2.98ms ± 0% 3.38ms ± 2% +13.49% (p=0.000 n=9+10)
RangeQuery/expr=changes(a_ten[1d]),steps=10-16 3.66ms ± 1% 4.02ms ± 1% +9.80% (p=0.000 n=10+9)
RangeQuery/expr=changes(a_ten[1d]),steps=100-16 10.5ms ± 0% 10.8ms ± 1% +3.08% (p=0.000 n=8+10)
RangeQuery/expr=changes(a_ten[1d]),steps=1000-16 77.6ms ± 1% 78.1ms ± 1% +0.58% (p=0.035 n=9+10)
RangeQuery/expr=changes(a_hundred[1d]),steps=1-16 30.4ms ± 2% 33.5ms ± 4% +10.18% (p=0.000 n=10+10)
RangeQuery/expr=changes(a_hundred[1d]),steps=10-16 37.1ms ± 2% 40.0ms ± 1% +7.98% (p=0.000 n=10+10)
RangeQuery/expr=changes(a_hundred[1d]),steps=100-16 105ms ± 1% 107ms ± 1% +1.92% (p=0.000 n=10+10)
RangeQuery/expr=changes(a_hundred[1d]),steps=1000-16 783ms ± 3% 775ms ± 1% -1.02% (p=0.019 n=9+9)
```
In summary, the runtime doesn't really improve with this change for
queries with just a few steps. For queries with many steps, this
commit essentially reinstates the old performance. This is good
because the many-step queries are the one that matter most (longest
absolute runtime).
In terms of allocations, though, this commit doesn't make a dent at
all (numbers not shown). The reason is that most of the allocations
happen in the sampleRingIterator (in the storage package), which has
to be addressed in a separate commit.
Signed-off-by: beorn7 <beorn@grafana.com>
* Use zeropool.Pool to workaround SA6002
I built a tiny library called https://github.com/colega/zeropool to
workaround the SA6002 staticheck issue.
While searching for the references of that SA6002 staticheck issues on
Github first results was Prometheus itself, with quite a lot of ignores
of it.
This changes the usages of `sync.Pool` to `zeropool.Pool[T]` where a
pointer is not available.
Also added a benchmark for HeadAppender Append/Commit when series
already exist, which is one of the most usual cases IMO, as I didn't find
any.
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Improve BenchmarkHeadAppender with more cases
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* A little copying is better than a little dependency
https://www.youtube.com/watch?v=PAAkCSZUG1c&t=9m28s
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Fix imports order
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Add license header
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Copyright should be on one of the first 3 lines
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Use require.Equal for testing
I don't depend on testify in my lib, but here we have it available.
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Avoid flaky test
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
* Also use zeropool for pointsPool in engine.go
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
---------
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
Rather than removing the previous implementation of SanitizeLabelName,
offer another version named SanitizeFullLabelName that achieved the
desired requirements, without breaking existing Prometheus code.
Update testing to validate correctness of new variant.
Signed-off-by: Nick Moore <nicholas.moore@grafana.com>
SanitizeLabelName was not correctly sanitizing label names that:
1. Started with a digit (0-9)
2. Were empty
This commit changes the santization code to catch both of these edge
cases and adds new tests to validate it works correctly in them both. In
the first case, a leading digit will be replaced with an underscore, and
in the latter, the function will return a single underscore.
Signed-off-by: Nick Moore <nicholas.moore@grafana.com>
Export `marshalTimestamp` and `marshalValue` functions by moving them under their own util package.
Signed-off-by: Miguel Ángel Ortuño <ortuman@gmail.com>
* Add runtime config to control native histogram ingestion
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Make the config into a CLI flag
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
Signed-off-by: Ganesh Vernekar <ganeshvern@gmail.com>
* Update go to 1.19, set min version to 1.18
Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>
* Update golangci-lint
Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>
Signed-off-by: Julien Pivotto <roidelapluie@o11y.eu>
* refactor: move from io/ioutil to io and os packages
* use fs.DirEntry instead of os.FileInfo after os.ReadDir
Signed-off-by: MOREL Matthieu <matthieu.morel@cnp.fr>
Per Julien's feedback on #10369, we're choosing to be consistent with
data types inside the stats structure (ints) rather than with the points
format that is part of the normal query responses (strings). We have
this option because this data cannot be NaN/Inf.
Signed-off-by: Andrew Bloomgarden <blmgrdn@amazon.com>
This exactly corresponds to the statistic compared against MaxSamples
during the course of query execution, so users can see how close their
queries are to a limit.
Co-authored-by: Harkishen Singh <harkishensingh@hotmail.com>
Co-authored-by: Andrew Bloomgarden <blmgrdn@amazon.com>
Signed-off-by: Andrew Bloomgarden <blmgrdn@amazon.com>
This allows other implementations to inject their own statistics that
they're gathering in data linked from the context.Context. For example,
Cortex can inject its stats.Stats value under the `cortex` key.
Signed-off-by: Andrew Bloomgarden <blmgrdn@amazon.com>
We always track total samples queried and add those to the standard set
of stats queries can report.
We also allow optionally tracking per-step samples queried. This must be
enabled both at the engine and query level to be tracked and rendered.
The engine flag is exposed via a Prometheus feature flag, while the
query flag is set when stats=all.
Co-authored-by: Alan Protasio <approtas@amazon.com>
Co-authored-by: Andrew Bloomgarden <blmgrdn@amazon.com>
Co-authored-by: Harkishen Singh <harkishensingh@hotmail.com>
Signed-off-by: Andrew Bloomgarden <blmgrdn@amazon.com>
* remove vfsgen usages
Signed-off-by: Jan Fajerski <jfajersk@redhat.com>
* web: use embed package for static assets
This requires go 1.16.
Signed-off-by: Jan Fajerski <jfajersk@redhat.com>
* circleci: drop go generate in web/ui
Signed-off-by: Jan Fajerski <jfajersk@redhat.com>
* Makefile: compress web assets before build
This commit add compression before (and decompression after) prometheus
is build. This ensures that gzipped assets are embeded in the prometheus
binary, if the builtinassets build tag is passed. If the build tag is
not passed this step is still executed but has no effect.
All this is executed in a subshell so that we can run the decompress
step even if the build step fails, but retain the exit code of promu.
This cleanup could also cover interrupts, but I left that out for now.
Signed-off-by: Jan Fajerski <jfajersk@redhat.com>
* Run gofumpt on all files
Getting golangci-lint errors when building on my laptop, possibly because I have newer version of gofumpt then what it was formatted with.
Run gofumpt -w -extra on all files as it will be needed in the future anyway.
* Update golangci-lint to v1.44.2
v1.44.0 upgraded gofumpt so bumping version in CI will help keep formatting correct for everyone
* Address golangci-lint error
Getting 'error-strings: error strings should not be capitalized or end with punctuation or a newline' from revive here.
Drop new line.
Signed-off-by: Łukasz Mierzwa <l.mierzwa@gmail.com>
* remove vfsgen usages
Signed-off-by: Jan Fajerski <jfajersk@redhat.com>
* web: use embed package for static assets
This requires go 1.16.
Signed-off-by: Jan Fajerski <jfajersk@redhat.com>
* circleci: drop go generate in web/ui
Signed-off-by: Jan Fajerski <jfajersk@redhat.com>
* Makefile: compress web assets before build
This commit add compression before (and decompression after) prometheus
is build. This ensures that gzipped assets are embeded in the prometheus
binary, if the builtinassets build tag is passed. If the build tag is
not passed this step is still executed but has no effect.
All this is executed in a subshell so that we can run the decompress
step even if the build step fails, but retain the exit code of promu.
This cleanup could also cover interrupts, but I left that out for now.
Signed-off-by: Jan Fajerski <jfajersk@redhat.com>
* [FIXME]: add new module dependency on common/assets and temp replace
Signed-off-by: Jan Fajerski <jfajersk@redhat.com>
This creates a new `model` directory and moves all data-model related
packages over there:
exemplar labels relabel rulefmt textparse timestamp value
All the others are more or less utilities and have been moved to `util`:
gate logging modetimevfs pool runtime
Signed-off-by: beorn7 <beorn@grafana.com>
* TSDB: demistify seriesRefs and ChunkRefs
The TSDB package contains many types of series and chunk references,
all shrouded in uint types. Often the same uint value may
actually mean one of different types, in non-obvious ways.
This PR aims to clarify the code and help navigating to relevant docs,
usage, etc much quicker.
Concretely:
* Use appropriately named types and document their semantics and
relations.
* Make multiplexing and demuxing of types explicit
(on the boundaries between concrete implementations and generic
interfaces).
* Casting between different types should be free. None of the changes
should have any impact on how the code runs.
TODO: Implement BlockSeriesRef where appropriate (for a future PR)
Signed-off-by: Dieter Plaetinck <dieter@grafana.com>
* feedback
Signed-off-by: Dieter Plaetinck <dieter@grafana.com>
* agent: demistify seriesRefs and ChunkRefs
Signed-off-by: Dieter Plaetinck <dieter@grafana.com>
* Create experimental circular buffer resize method, benchmarks
Signed-off-by: Martin Disibio <mdisibio@gmail.com>
* Optimize exemplar resize to only replay as many exemplars as needed
Signed-off-by: Martin Disibio <mdisibio@gmail.com>
* More comments, benchmark AddExemplar
Signed-off-by: Martin Disibio <mdisibio@gmail.com>
* optimizations
Signed-off-by: Martin Disibio <mdisibio@gmail.com>
* comment
Signed-off-by: Martin Disibio <mdisibio@gmail.com>
* Slight refactor of resize benchmark + make use of resize via runtime
reloadable storage config.
Signed-off-by: Callum Styan <callumstyan@gmail.com>
* Some more config related changes.
Signed-off-by: Callum Styan <callumstyan@gmail.com>
* Address some review comments.
Signed-off-by: Callum Styan <callumstyan@gmail.com>
* Address more review comments.
Signed-off-by: Callum Styan <callumstyan@gmail.com>
* Refactor to remove usage of noopExemplarStorage and avoid race condition
when resizing from Head code.
Signed-off-by: Callum Styan <callumstyan@gmail.com>
* Fix or add comments to clarify some of the new behaviour.
Signed-off-by: Callum Styan <callumstyan@gmail.com>
* fix potential panics related to negative exemplar buffer lengths
Signed-off-by: Callum Styan <callumstyan@gmail.com>
Co-authored-by: Callum Styan <callumstyan@gmail.com>
* Added walreplay API endpoint
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Added starting page to react-ui
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Documented the new endpoint
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fixed typos
Signed-off-by: Levi Harrison <git@leviharrison.dev>
Co-authored-by: Julius Volz <julius.volz@gmail.com>
* Removed logo
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed isResponding to isUnexpected
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed width of progress bar
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed width of progress bar
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Added DB stats object
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Updated starting page to work with new fields
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil (pt. 2)
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil (pt. 3)
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil (and also implementing a method this time) (pt. 4)
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil (and also implementing a method this time) (pt. 5)
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed const to let
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Passing nil (pt. 6)
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Remove SetStats method
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Added comma
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed api
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed to triple equals
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fixed data response types
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Don't return pointer
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Changed version
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fixed interface issue
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fixed pointer
Signed-off-by: Levi Harrison <git@leviharrison.dev>
* Fixed copying lock value error
Signed-off-by: Levi Harrison <git@leviharrison.dev>
Co-authored-by: Julius Volz <julius.volz@gmail.com>
This go routing uses a ticker to stop. This is prompt to create false
positives in tests failures. It is also unexported so let's threat that
as a k8s internal. Therefore, let's ignore it in goleak.
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
* Testify: move to require
Moving testify to require to fail tests early in case of errors.
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
* More moves
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
* Implement go leak test for promql
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
* Implement go leak test for Consul SD
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
* Implement go leak test in discovery manager
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
Previously it could return error if RemoteAddr didn't
have correct format, but since this field has no specified
format, that was little too strict.
Signed-off-by: Peter Štibraný <peter.stibrany@grafana.com>
This is part of https://github.com/prometheus/prometheus/pull/5882 that can be done to simplify things.
All todos I added will be fixed in follow up PRs.
* querier.Querier, querier.Appender, querier.SeriesSet, and querier.Series interfaces merged
with storage interface.go. All imports that.
* querier.SeriesIterator replaced by chunkenc.Iterator
* Added chunkenc.Iterator.Seek method and tests for xor implementation (?)
* Since we properly handle SelectParams for Select methods I adjusted min max
based on that. This should help in terms of performance for queries with functions like offset.
* added Seek to deletedIterator and test.
* storage/tsdb was removed as it was only a unnecessary glue with incompatible structs.
No logic was changed, only different source of abstractions, so no need for benchmarks.
Signed-off-by: Bartlomiej Plotka <bwplotka@gmail.com>
Also improves TestPopulateLabels: testutil.ErrorEqual just returned a
bool without failing the test.
Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>
* Extra promlint rules for Issue 5453
* broaden type name and camelCase checks
* Expand unit test to catch non base units
* Use only celsius as the base unit for temperature
* Remove candela and moles from the unit check
Signed-off-by: David Ellis <ellisda@gmail.com>
i) Uses the more idiomatic Wrap and Wrapf methods for creating nested errors.
ii) Fixes some incorrect usages of fmt.Errorf where the error messages don't have any formatting directives.
iii) Does away with the use of fmt package for errors in favour of pkg/errors
Signed-off-by: tariqibrahim <tariq181290@gmail.com>
* *: use latest release of staticcheck
It also fixes a couple of things in the code flagged by the additional
checks.
Signed-off-by: Simon Pasquier <spasquie@redhat.com>
* Use official release of staticcheck
Also run 'go list' before staticcheck to avoid failures when downloading packages.
Signed-off-by: Simon Pasquier <spasquie@redhat.com>
Julius Volz