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fix(approx_topk): Map approx_topk operation in all cases #16131

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merged 4 commits into from
Feb 14, 2025
Merged

fix(approx_topk): Map approx_topk operation in all cases #16131

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8508cc7
fix(approx_topk): Always rewrite approx_topk
benclive Feb 6, 2025
8b259f8
Add comparison to shardable ops
benclive Feb 6, 2025
2877839
Extract duplicate logic
benclive Feb 6, 2025
967ad7a
Remove comparison from shardable
benclive Feb 7, 2025
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28 changes: 28 additions & 0 deletions pkg/logql/shardmapper.go
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Original file line number Diff line number Diff line change
Expand Up @@ -367,6 +367,34 @@ func (m ShardMapper) mapVectorAggregationExpr(expr *syntax.VectorAggregationExpr
}
return expr, exprStats.Bytes, nil
}
} else {
// if this AST contains unshardable operations, we still need to rewrite some operations (e.g. approx_topk) as if it had 0 shards as they are not supported on the querier
level.Error(util_log.Logger).Log(
"msg", "unshardable operation which is not supported by downstream querier",
"operation", expr.Operation,
)
switch expr.Operation {
case syntax.OpTypeApproxTopK:
_, bytesPerShard, err := m.shards.Resolver().Shards(expr)
if err != nil {
return nil, 0, err
}

countMinSketchExpr := syntax.MustClone(expr)
countMinSketchExpr.Operation = syntax.OpTypeCountMinSketch
countMinSketchExpr.Params = 0

return &syntax.VectorAggregationExpr{
Left: &CountMinSketchEvalExpr{
downstreams: []DownstreamSampleExpr{{
SampleExpr: countMinSketchExpr,
}},
},
Grouping: expr.Grouping,
Operation: syntax.OpTypeTopK,
Params: expr.Params,
}, bytesPerShard, nil
}
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}

// if this AST contains unshardable operations, don't shard this at this level,
Expand Down
145 changes: 144 additions & 1 deletion pkg/logql/shardmapper_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -245,7 +245,7 @@ func TestMappingStrings(t *testing.T) {
sum by (foo_extracted) (
downstream<sumby(foo_extracted)(quantile_over_time(0.95,{foo="baz"}|logfmt|unwrapfoo_extracted|__error__=""[5m])),shard=0_of_2>++downstream<sumby(foo_extracted)(quantile_over_time(0.95,{foo="baz"}|logfmt|unwrapfoo_extracted|__error__=""[5m])),shard=1_of_2>
)
/
/
sum by (foo_extracted) (
downstream<countby(foo_extracted)(quantile_over_time(0.95,{foo="baz"}|logfmt|unwrapfoo_extracted|__error__=""[5m])),shard=0_of_2>++downstream<countby(foo_extracted)(quantile_over_time(0.95,{foo="baz"}|logfmt|unwrapfoo_extracted|__error__=""[5m])),shard=1_of_2>
)
Expand Down Expand Up @@ -652,6 +652,52 @@ func TestMapping(t *testing.T) {
},
},
},
{
in: `rate({foo="bar"}[5m]) > 3`,
expr: &syntax.BinOpExpr{
Op: syntax.OpTypeGT,
SampleExpr: &ConcatSampleExpr{
DownstreamSampleExpr: DownstreamSampleExpr{
shard: NewPowerOfTwoShard(index.ShardAnnotation{
Shard: 0,
Of: 2,
}).Bind(nil),
SampleExpr: &syntax.RangeAggregationExpr{
Operation: syntax.OpRangeTypeRate,
Left: &syntax.LogRangeExpr{
Left: &syntax.MatchersExpr{
Mts: []*labels.Matcher{mustNewMatcher(labels.MatchEqual, "foo", "bar")},
},
Interval: 5 * time.Minute,
},
},
},
next: &ConcatSampleExpr{
DownstreamSampleExpr: DownstreamSampleExpr{
shard: NewPowerOfTwoShard(index.ShardAnnotation{
Shard: 1,
Of: 2,
}).Bind(nil),
SampleExpr: &syntax.RangeAggregationExpr{
Operation: syntax.OpRangeTypeRate,
Left: &syntax.LogRangeExpr{
Left: &syntax.MatchersExpr{
Mts: []*labels.Matcher{mustNewMatcher(labels.MatchEqual, "foo", "bar")},
},
Interval: 5 * time.Minute,
},
},
},
next: nil,
},
},
RHS: &syntax.LiteralExpr{Val: 3},
Opts: &syntax.BinOpOptions{
ReturnBool: false,
VectorMatching: &syntax.VectorMatching{},
},
},
},
{
in: `count_over_time({foo="bar"}[5m])`,
expr: &ConcatSampleExpr{
Expand Down Expand Up @@ -833,6 +879,103 @@ func TestMapping(t *testing.T) {
},
},
},
{
in: `approx_topk(3, rate({foo="bar"}[5m]) > 3)`,
expr: &syntax.VectorAggregationExpr{
Grouping: &syntax.Grouping{},
Params: 3,
Operation: syntax.OpTypeTopK,
Left: &CountMinSketchEvalExpr{
downstreams: []DownstreamSampleExpr{
{
shard: NewPowerOfTwoShard(index.ShardAnnotation{
Shard: 0,
Of: 2,
}).Bind(nil),
SampleExpr: &syntax.VectorAggregationExpr{
Operation: syntax.OpTypeCountMinSketch,
Left: &syntax.BinOpExpr{
Op: syntax.OpTypeGT,
SampleExpr: &syntax.RangeAggregationExpr{
Operation: syntax.OpRangeTypeRate,
Left: &syntax.LogRangeExpr{
Left: &syntax.MatchersExpr{
Mts: []*labels.Matcher{mustNewMatcher(labels.MatchEqual, "foo", "bar")},
},
Interval: 5 * time.Minute,
},
},
RHS: &syntax.LiteralExpr{Val: 3},
Opts: &syntax.BinOpOptions{
ReturnBool: false,
VectorMatching: &syntax.VectorMatching{},
},
},
Grouping: &syntax.Grouping{},
},
},
{
shard: NewPowerOfTwoShard(index.ShardAnnotation{
Shard: 1,
Of: 2,
}).Bind(nil),
SampleExpr: &syntax.VectorAggregationExpr{
Operation: syntax.OpTypeCountMinSketch,
Left: &syntax.BinOpExpr{
Op: syntax.OpTypeGT,
SampleExpr: &syntax.RangeAggregationExpr{
Operation: syntax.OpRangeTypeRate,
Left: &syntax.LogRangeExpr{
Left: &syntax.MatchersExpr{
Mts: []*labels.Matcher{mustNewMatcher(labels.MatchEqual, "foo", "bar")},
},
Interval: 5 * time.Minute,
},
},
RHS: &syntax.LiteralExpr{Val: 3},
Opts: &syntax.BinOpOptions{
ReturnBool: false,
VectorMatching: &syntax.VectorMatching{},
},
},
Grouping: &syntax.Grouping{},
},
},
},
},
},
},
{
// A contrived query that is not shardable: but we must rewrite `approx_topk` as if it had 0 shards because the approx_topk operation is not supported on the querier
in: `approx_topk(3, topk(5, rate({foo="bar"}[5m])))`,
expr: &syntax.VectorAggregationExpr{
Left: &CountMinSketchEvalExpr{
downstreams: []DownstreamSampleExpr{{
SampleExpr: &syntax.VectorAggregationExpr{
Operation: syntax.OpTypeCountMinSketch,
Left: &syntax.VectorAggregationExpr{Operation: syntax.OpTypeTopK,
Params: 5,
Left: &syntax.RangeAggregationExpr{
Operation: syntax.OpRangeTypeRate,
Left: &syntax.LogRangeExpr{
Left: &syntax.MatchersExpr{
Mts: []*labels.Matcher{mustNewMatcher(labels.MatchEqual, "foo", "bar")},
},
Interval: 5 * time.Minute,
},
},
Grouping: &syntax.Grouping{},
},
Grouping: &syntax.Grouping{},
},
shard: nil,
}},
},
Grouping: &syntax.Grouping{},
Operation: syntax.OpTypeTopK,
Params: 3,
},
},
{
in: `count(rate({foo="bar"}[5m]))`,
expr: &syntax.VectorAggregationExpr{
Expand Down
6 changes: 6 additions & 0 deletions pkg/logql/syntax/ast.go
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Expand Up @@ -2291,6 +2291,12 @@ var shardableOps = map[string]bool{
// binops - arith
OpTypeAdd: true,
OpTypeMul: true,

// binops - comparison
OpTypeGT: true,
OpTypeGTE: true,
OpTypeLT: true,
OpTypeLTE: true,
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Are we sure these are shardable? Is this an orthogonal change to the above?

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As far as I understand, we should treat them the same way as the arithmetic operations above. There's no special logic for those operations, they just get mapped to queriers and combined as usual.
I don't think sharding a approx_topk query containing a comparison will change the result, as far as I can see, though I don't have any proof beyond the existing tests that it is valid to do so.
If you prefer I can remove this change and those types of queries will fall into the "not shardable" logic instead. I've tested it locally and it does seem to give correct results - WDYT?

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@jeschkies jeschkies Feb 6, 2025 •
edited
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Hm, so I'd push the operator don to each shard because it's filtering out the metrics. Does that makes sense? As in:

count_over_timer({...}[...]) > 0

should be

downstream<count_over_timer({..., __shard__=0}[...]) > 0>
++ ...
++ downstream<count_over_timer({..., __shard__=n}[...]) > 0>

and not

(downstream<count_over_timer({..., __shard__=0}[...])> 
 ++ ...
 ++ downstream<count_over_timer({..., __shard__=n}[...])>
) > 0

I think sharding these is a little more evolved and should be a separarte PR.

}

type MatcherRange struct {
Expand Down