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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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134 changes: 74 additions & 60 deletions pkg/logql/shardmapper.go
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -293,66 +293,7 @@ func (m ShardMapper) mapVectorAggregationExpr(expr *syntax.VectorAggregationExpr
return nil, 0, fmt.Errorf("approx_topk is not enabled. See -limits.shard_aggregations")
}

// TODO(owen-d): integrate bounded sharding with approx_topk
// I'm not doing this now because it uses a separate code path and may not handle
// bounded shards in the same way
shards, bytesPerShard, err := m.shards.Resolver().Shards(expr)
if err != nil {
return nil, 0, err
}

// approx_topk(k, inner) ->
// topk(
// k,
// eval_cms(
// __count_min_sketch__(inner, shard=1) ++ __count_min_sketch__(inner, shard=2)...
// )
// )

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

// Even if this query is not sharded the user wants an approximation. This is helpful if some
// inferred label has a very high cardinality. Note that the querier does not support CountMinSketchEvalExpr
// which is why it's evaluated on the front end.
if shards == 0 {
return &syntax.VectorAggregationExpr{
Left: &CountMinSketchEvalExpr{
downstreams: []DownstreamSampleExpr{{
SampleExpr: countMinSketchExpr,
}},
},
Grouping: expr.Grouping,
Operation: syntax.OpTypeTopK,
Params: expr.Params,
}, bytesPerShard, nil
}

downstreams := make([]DownstreamSampleExpr, 0, shards)
for shard := 0; shard < shards; shard++ {
s := NewPowerOfTwoShard(index.ShardAnnotation{
Shard: uint32(shard),
Of: uint32(shards),
})
downstreams = append(downstreams, DownstreamSampleExpr{
shard: &ShardWithChunkRefs{
Shard: s,
},
SampleExpr: countMinSketchExpr,
})
}

sharded := &CountMinSketchEvalExpr{
downstreams: downstreams,
}

return &syntax.VectorAggregationExpr{
Left: sharded,
Grouping: expr.Grouping,
Operation: syntax.OpTypeTopK,
Params: expr.Params,
}, bytesPerShard, nil
return m.mapApproxTopk(expr, false)
default:
// this should not be reachable. If an operation is shardable it should
// have an optimization listed. Nonetheless, we log this as a warning
Expand All @@ -367,6 +308,16 @@ 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
switch expr.Operation {
case syntax.OpTypeApproxTopK:
level.Error(util_log.Logger).Log(
"msg", "encountered unshardable approx_topk operation",
"operation", expr.Operation,
)
return m.mapApproxTopk(expr, true)
}
}

// if this AST contains unshardable operations, don't shard this at this level,
Expand All @@ -388,6 +339,69 @@ func (m ShardMapper) mapVectorAggregationExpr(expr *syntax.VectorAggregationExpr
}, bytesPerShard, nil
}

func (m ShardMapper) mapApproxTopk(expr *syntax.VectorAggregationExpr, forceNoShard bool) (*syntax.VectorAggregationExpr, uint64, error) {
// TODO(owen-d): integrate bounded sharding with approx_topk
// I'm not doing this now because it uses a separate code path and may not handle
// bounded shards in the same way
shards, bytesPerShard, err := m.shards.Resolver().Shards(expr)
if err != nil {
return nil, 0, err
}

// approx_topk(k, inner) ->
// topk(
// k,
// eval_cms(
// __count_min_sketch__(inner, shard=1) ++ __count_min_sketch__(inner, shard=2)...
// )
// )

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

// Even if this query is not sharded the user wants an approximation. This is helpful if some
// inferred label has a very high cardinality. Note that the querier does not support CountMinSketchEvalExpr
// which is why it's evaluated on the front end.
if shards == 0 || forceNoShard {
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Adding || forceNoShard is the only effective change, right?

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Yes, nothing else has changed in this function otherwise

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

downstreams := make([]DownstreamSampleExpr, 0, shards)
for shard := 0; shard < shards; shard++ {
s := NewPowerOfTwoShard(index.ShardAnnotation{
Shard: uint32(shard),
Of: uint32(shards),
})
downstreams = append(downstreams, DownstreamSampleExpr{
shard: &ShardWithChunkRefs{
Shard: s,
},
SampleExpr: countMinSketchExpr,
})
}

sharded := &CountMinSketchEvalExpr{
downstreams: downstreams,
}

return &syntax.VectorAggregationExpr{
Left: sharded,
Grouping: expr.Grouping,
Operation: syntax.OpTypeTopK,
Params: expr.Params,
}, bytesPerShard, nil
}

func (m ShardMapper) mapLabelReplaceExpr(expr *syntax.LabelReplaceExpr, r *downstreamRecorder, topLevel bool) (syntax.SampleExpr, uint64, error) {
subMapped, bytesPerShard, err := m.Map(expr.Left, r, topLevel)
if err != nil {
Expand Down
115 changes: 114 additions & 1 deletion pkg/logql/shardmapper_test.go
View file
Open in desktop
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 +879,73 @@ 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: 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