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feat(Query): Add random keyword in DQL #7693

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merged 3 commits into from
Apr 25, 2021
Merged

feat(Query): Add random keyword in DQL #7693

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63aba94
add "random" keyword in GQL for selecting random nodes in graph
Samyak2 Apr 7, 2021
6252918
random query (#7693) - remove duplicates in result and rename random_
Samyak2 Apr 13, 2021
558ea5d
random query (#7693) - simpler random selection
Samyak2 Apr 22, 2021
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4 changes: 2 additions & 2 deletions gql/parser.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2595,7 +2595,7 @@ func parseLanguageList(it *lex.ItemIterator) ([]string, error) {

func validKeyAtRoot(k string) bool {
switch k {
case "func", "orderasc", "orderdesc", "first", "offset", "after":
case "func", "orderasc", "orderdesc", "first", "offset", "after", "random":
return true
case "from", "to", "numpaths", "minweight", "maxweight":
// Specific to shortest path
Expand All @@ -2609,7 +2609,7 @@ func validKeyAtRoot(k string) bool {
// Check for validity of key at non-root nodes.
func validKey(k string) bool {
switch k {
case "orderasc", "orderdesc", "first", "offset", "after":
case "orderasc", "orderdesc", "first", "offset", "after", "random":
return true
}
return false
Expand Down
49 changes: 48 additions & 1 deletion query/query.go
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Original file line number Diff line number Diff line change
Expand Up @@ -20,6 +20,7 @@ import (
"context"
"fmt"
"math"
"math/rand"
"sort"
"strconv"
"strings"
Expand Down Expand Up @@ -114,6 +115,8 @@ type params struct {
Count int
// Offset is the value of the "offset" parameter.
Offset int
// Random is the value of the "random" parameter
Random int
// AfterUID is the value of the "after" parameter.
AfterUID uint64
// DoCount is true if the count of the predicate is requested instead of its value.
Expand Down Expand Up @@ -745,6 +748,15 @@ func (args *params) fill(gq *gql.GraphQuery) error {
}
args.Count = int(first)
}

if v, ok := gq.Args["random"]; ok {
random_, err := strconv.ParseInt(v, 0, 32)
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if err != nil {
return err
}
args.Random = int(random_)
}

return nil
}

Expand Down Expand Up @@ -2298,6 +2310,13 @@ func ProcessGraph(ctx context.Context, sg, parent *SubGraph, rch chan error) {
}
}

if sg.Params.Random > 0 {
if err = sg.applyRandom(ctx); err != nil {
rch <- err
return
}
}

// Here we consider handling count with filtering. We do this after
// pagination because otherwise, we need to do the count with pagination
// taken into account. For example, a PL might have only 50 entries but the
Expand Down Expand Up @@ -2395,6 +2414,34 @@ func ProcessGraph(ctx context.Context, sg, parent *SubGraph, rch chan error) {
rch <- childErr
}

// applies "random" to lists inside uidMatrix
// Params.Random number of nodes are selected
// duplicates are not removed i.e., random selection by replacement is done
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We should not have duplicate results. I'd suggest having some map to keep track of what all we have already picked to randomly pick n unique results.

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Okay, I'll do this, along with the filters application.

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I don't think you need to do anything for filters. You are already doing the random selection after filter application and pagination.

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Oh okay. That explains why I couldn't figure out how to do it by looking at pagination xD.

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I have pushed a commit fixing these.

To remove duplicates, I had to:

  • introduce a new struct UidKey to store the index of a UID in the matrix
  • calculate total number of nodes and check if required number of nodes is less than that. If it's not, return all the nodes.

Because of the condition if sg.Params.Random >= totalNodes at line 2440, when the required number of nodes (sg.Params.Random) is equal to the total number of nodes, all of the nodes are returned without any processing. I did this thinking of it as an optimization (because there will be many overlaps in random numbers when only a few nodes are left to be selected). But I just realized that this will make it so that the order is not randomized when sg.Params.Random == totalNodes. Should I fix this to do the random selection even when all the nodes have to be selected?

// TODO: error handling here
func (sg *SubGraph) applyRandom(ctx context.Context) error {
sg.updateUidMatrix()

// store row id -> new uid list mapping
newUids := make(map[int][]uint64)
for i := 0; i < sg.Params.Random; i++ {
randomIdx := rand.Intn(len(sg.uidMatrix))
randomIdy := rand.Intn(len(sg.uidMatrix[randomIdx].Uids))

if newUids[randomIdx] == nil {
newUids[randomIdx] = make([]uint64, 0)
}

newUids[randomIdx] = append(newUids[randomIdx], sg.uidMatrix[randomIdx].Uids[randomIdy])
}

for idx, uids := range newUids {
sg.uidMatrix[idx].Uids = uids
}

sg.DestMap = codec.Merge(sg.uidMatrix)
return nil
}

// applyPagination applies count and offset to lists inside uidMatrix.
func (sg *SubGraph) applyPagination(ctx context.Context) error {
if sg.Params.Count == 0 && sg.Params.Offset == 0 { // No pagination.
Expand Down Expand Up @@ -2638,7 +2685,7 @@ func (sg *SubGraph) sortAndPaginateUsingVar(ctx context.Context) error {
func isValidArg(a string) bool {
switch a {
case "numpaths", "from", "to", "orderasc", "orderdesc", "first", "offset", "after", "depth",
"minweight", "maxweight":
"minweight", "maxweight", "random":
return true
}
return false
Expand Down