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Add metric for showing the errant GTIDs in VTOrc #13281

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merged 5 commits into from
Jun 15, 2023
Merged

Add metric for showing the errant GTIDs in VTOrc #13281

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2443ec1
feat: add metric for errant gtid
GuptaManan100 Jun 9, 2023
08b3ebe
feat: update the errant gtid map always, so that once errant gtids ar…
GuptaManan100 Jun 9, 2023
088f559
feat: fix the test to match the new expectations
GuptaManan100 Jun 9, 2023
84098ee
feat: add mutex to protect the access to the map storing errant gtids
GuptaManan100 Jun 14, 2023
0fe73a4
feat: update the errant gtid map in a goroutine
GuptaManan100 Jun 14, 2023
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20 changes: 20 additions & 0 deletions go/test/endtoend/vtorc/api/api_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,9 @@ limitations under the License.
package api

import (
"encoding/json"
"fmt"
"reflect"
"testing"
"time"

Expand Down Expand Up @@ -197,5 +199,23 @@ func TestAPIEndpoints(t *testing.T) {
require.NoError(t, err)
assert.Equal(t, 400, status, resp)
assert.Equal(t, "Filtering by shard without keyspace isn't supported\n", resp)

// Also verify that the metric for errant GTIDs is reporting the correct information.
_, resp, err = utils.MakeAPICall(t, vtorc, "/debug/vars")
require.NoError(t, err)
resultMap := make(map[string]any)
err = json.Unmarshal([]byte(resp), &resultMap)
require.NoError(t, err)
errantGTIDMap := reflect.ValueOf(resultMap["ErrantGtidMap"])
errantGtidTablets := errantGTIDMap.MapKeys()
require.Len(t, errantGtidTablets, 3)

errantGTIDinReplica := ""
for _, tabletKey := range errantGtidTablets {
if tabletKey.String() == replica.Alias {
errantGTIDinReplica = errantGTIDMap.MapIndex(tabletKey).Interface().(string)
}
}
require.NotEmpty(t, errantGTIDinReplica)
})
}
10 changes: 10 additions & 0 deletions go/vt/vtorc/inst/instance_dao.go
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Expand Up @@ -31,6 +31,7 @@ import (
"github.com/rcrowley/go-metrics"
"github.com/sjmudd/stopwatch"

"vitess.io/vitess/go/stats"
"vitess.io/vitess/go/vt/external/golib/sqlutils"

vitessmysql "vitess.io/vitess/go/mysql"
Expand All @@ -56,6 +57,10 @@ const (
var instanceReadChan = make(chan bool, backendDBConcurrency)
var instanceWriteChan = make(chan bool, backendDBConcurrency)

var (
errantGtidMap = make(map[string]string)
)

// Constant strings for Group Replication information
// See https://dev.mysql.com/doc/refman/8.0/en/replication-group-members-table.html for additional information.
const (
Expand Down Expand Up @@ -88,6 +93,9 @@ func init() {
_ = metrics.Register("instance.write", writeInstanceCounter)
_ = writeBufferLatency.AddMany([]string{"wait", "write"})
writeBufferLatency.Start("wait")
stats.NewStringMapFuncWithMultiLabels("ErrantGtidMap", "Metric to track the errant GTIDs detected by VTOrc", []string{"TabletAlias"}, "ErrantGtid", func() map[string]string {
return errantGtidMap
})

go initializeInstanceDao()
}
Expand Down Expand Up @@ -429,6 +437,8 @@ Cleanup:
instance.GtidErrant, err = vitessmysql.Subtract(redactedExecutedGtidSet.String(), redactedPrimaryExecutedGtidSet.String())
}
}
// update the errant gtid map
errantGtidMap[topoproto.TabletAliasString(tablet.Alias)] = instance.GtidErrant
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Could we be writing to and reading (the metric) from the map concurrently? In that case we will need to synchronize the accesses.

Also could there be multiple concurrent writes to this map? I see handleDiscoveryRequests() is discovering instances in parallel.

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This map is only used for a metric, so it should be okay to read and write concurrently to it, right? I can add locking around it, but I don't see the need for it.

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I have never seen this in practice, but as per 1.6+ https://go.dev/doc/go1.6 says, :

Runtime
The runtime has added lightweight, best-effort detection of concurrent misuse of maps. As always, if one goroutine is writing to a map, no other goroutine should be reading or writing the map concurrently. If the runtime detects this condition, it prints a diagnosis and crashes the program. The best way to find out more about the problem is to run the program under the race detector, which will more reliably identify the race and give more detail.

Another reference: https://stackoverflow.com/questions/36167200/how-safe-are-golang-maps-for-concurrent-read-write-operations which shows a runtime panic can occur.

I think if you had a unit test around this the race detector would have failed it.

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Agreed with @rohit-nayak-ps, this requires synchronization.

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Gotcha, I'll add synchronization then.

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Added.

}

latency.Stop("instance")
Expand Down
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