This PR is a reference implementation of the proposal described in #10420.
In addition to what described in #10420, in this PR I've introduced labels.StableHash(). The idea is to offer an hashing function which doesn't change over time, and that's used by query sharding in order to get a stable behaviour over time. The implementation of labels.StableHash() is the hashing function used by Prometheus before stringlabels, and what's used by Grafana Mimir for query sharding (because built before stringlabels was a thing).
Follow up work
As mentioned in #10420, if this PR is accepted I'm also open to upload another foundamental piece used by Grafana Mimir query sharding to accelerate the query execution: an optional, configurable and fast in-memory cache for the series hashes.
Signed-off-by: Marco Pracucci <marco@pracucci.com>
* tsdb/{index,compact}: allow using custom postings encoding format
We would like to experiment with a different postings encoding format in
Thanos so in this change I am proposing adding another argument to
`NewWriter` which would allow users to change the format if needed.
Also, wire the leveled compactor so that it would be possible to change
the format there too.
Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
* tsdb/compact: use a struct for leveled compactor options
As discussed on Slack, let's use a struct for the options in leveled
compactor.
Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
* tsdb: make changes after Bryan's review
- Make changes less intrusive
- Turn the postings encoder type into a function
- Add NewWriterWithEncoder()
Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
---------
Signed-off-by: Giedrius Statkevičius <giedrius.statkevicius@vinted.com>
It's faster.
Note change to test - instead of requiring that the data structure is
identical to `EmptyPostings()`, check that calling `Next()` returns
false, which implies it was empty.
Also the check for context cancellation during initialization was
removed. Initialization should be a small portion of the work done
during merge, so it's not worth plumbing a context argument through.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Drop context argument from tsdb/index.Symbols.Lookup since lookup
should be fast and the context checking is a performance hit.
Signed-off-by: Arve Knudsen <arve.knudsen@gmail.com>
On a 32 bit architecture the size of int is 32 bits. Thus converting from
int64, uint64 can overflow it and flip the sign.
Try for yourself in playground:
package main
import "fmt"
func main() {
x := int64(0x1F0000001)
y := int64(1)
z := int32(x - y) // numerically this is 0x1F0000000
fmt.Printf("%v\n", z)
}
Prints -268435456 as if x was smaller.
Followup to #12650
Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>
Reverts change from https://github.com/prometheus/prometheus/pull/12906
The benchmarks show that it's slower when intersecting, which is a
common usage for ListPostings (when intersecting matchers from Head)
(old is before #12906, new is #12906):
│ old │ new │
│ sec/op │ sec/op vs base │
Intersect/LongPostings1-16 20.54µ ± 1% 21.11µ ± 1% +2.76% (p=0.000 n=20)
Intersect/LongPostings2-16 51.03m ± 1% 52.40m ± 2% +2.69% (p=0.000 n=20)
Intersect/ManyPostings-16 194.2m ± 3% 332.1m ± 1% +71.00% (p=0.000 n=20)
geomean 5.882m 7.161m +21.74%
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
It's implicit, but should be explicit. It is invalid to call At() after
a failed call to Next() or Seek().
Following up on https://github.com/prometheus/prometheus/pull/12906
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
The Next() call of ListPostings() was updating two values, while we can
just update the position. This is up to 30% faster for high number of
Postings.
goos: linux
goarch: amd64
pkg: github.com/prometheus/prometheus/tsdb/index
cpu: 11th Gen Intel(R) Core(TM) i7-11700K @ 3.60GHz
│ old │ new │
│ sec/op │ sec/op vs base │
ListPostings/count=100-16 819.2n ± 0% 732.6n ± 0% -10.58% (p=0.000 n=20)
ListPostings/count=1000-16 2.685µ ± 1% 2.017µ ± 0% -24.88% (p=0.000 n=20)
ListPostings/count=10000-16 21.43µ ± 1% 14.81µ ± 0% -30.91% (p=0.000 n=20)
ListPostings/count=100000-16 209.4µ ± 1% 143.3µ ± 0% -31.55% (p=0.000 n=20)
ListPostings/count=1000000-16 2.086m ± 1% 1.436m ± 1% -31.18% (p=0.000 n=20)
geomean 29.02µ 21.41µ -26.22%
We're talking about microseconds here, but they just keep adding.
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
Problem:
LabelValueStats - This will provide a list of the label names and memory used in bytes.
It is calculated by adding the length of all values for a given label name.
But internally Prometheus stores the name and the value independently for each series.
Solution:
MemPostings struct maintains the values to seriesRef map which is used
to get the number of series which contains the label values.
Using that LabelValueStats is calculated as: seriesCnt * len(value
name)
Signed-off-by: Baskar Shanmugam <baskar.shanmugam.career@gmail.com>
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>
In the head and in v1 postings on disk, it makes no difference whether
postings are sorted. Only for v2 does the code step through in order.
So, move the sorting to where it is required, and thus skip it entirely
in the head.
Label values in on-disk blocks are already sorted, but `slices.Sort` is
very fast on already-sorted data so we don't bother checking.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
This allocates memory for all the returned values, which skews the
result. We aren't trying to benchmark `ExpandPostings`, so just step
through all the values without storing them to consume them.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Previously all the postings constructed were consumed on the first
iteration, so subsequent iterations did no work.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Instead of passing in a `ScratchBuilder` and `Labels`, just pass the
builder and the caller can extract labels from it. In many cases the
caller didn't use the Labels value anyway.
Now in `Labels.ScratchBuilder` we need a slightly different API: one
to assign what will be the result, instead of overwriting some other
`Labels`. This is safer and easier to reason about.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
This necessitates a change to the `tsdb.IndexReader` interface:
`index.Reader` is used from multiple goroutines concurrently, so we
can't have state in it.
We do retain a `ScratchBuilder` in `blockBaseSeriesSet` which is
iterator-like.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
* Add BenchmarkOpenBlock
* Use specific types when reading offset table
Instead of reading a generic-ish []string, we can read a generic type
which would be specifically labels.Label.
This avoid allocating a slice that escapes to the heap, making it both
faster and more efficient in terms of memory management.
* Update error message for unexpected number of keys
* s/posting offset table/postings offset table/
* Remove useless lastKey assignment
* Use two []bytes vars, simplify
Applied PR feedback: removed generics, moved the label indices reading
to that specific test as we're not using it in production anyway, we're
just testing what we've just built.
Also using two []bytes variables for name and value that use the backing
buffer instead of using strings, this reduces allocations a lot as we
only copy them when we store them (this is optimized by the compiler).
* Fix the dumb bug
Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>
Co-authored-by: Marco Pracucci <marco@pracucci.com>
Use new experimental package `golang.org/x/exp/slices`.
slices.Sort works on values that are directly comparable, like ints,
so avoids the overhad of an interface call to `.Less()`.
Left tests unchanged, because they don't need the speed and it may be
a cross-check that slices.Sort gives the same answer.
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Use new experimental package `golang.org/x/exp/slices`.
Some of the speedup comes from comparing SeriesRef (which is an int64)
directly rather than through an interface `.Less()` call; some comes
from exp/slices using "pattern-defeating quicksort(pdqsort)".
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
Signed-off-by: Bryan Boreham <bjboreham@gmail.com>
