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https://issues.apache.org/jira/browse/BEAM-4727?focusedWorklogId=121964&page=com.atlassian.jira.plugin.system.issuetabpanels:worklog-tabpanel#worklog-121964
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ASF GitHub Bot logged work on BEAM-4727:
----------------------------------------
Author: ASF GitHub Bot
Created on: 11/Jul/18 17:17
Start Date: 11/Jul/18 17:17
Worklog Time Spent: 10m
Work Description: lostluck commented on a change in pull request #5884:
[BEAM-4727] Re-use metric context throughout bundle
URL: https://github.com/apache/beam/pull/5884#discussion_r201773998
##########
File path: sdks/go/pkg/beam/core/metrics/metrics.go
##########
@@ -69,18 +69,58 @@ type ctxKey string
const bundleKey ctxKey = "beam:bundle"
const ptransformKey ctxKey = "beam:ptransform"
+// context is a caching context since reads & writes are expensive.
+type beamCtx struct {
+ context.Context
+ bundleID, ptransformID string
+}
+
+// Lift the keys value for faster lookups when not available.
+func (ctx *beamCtx) Value(key interface{}) interface{} {
+ switch key {
+ case bundleKey:
+ if ctx.bundleID == "" {
+ if id := ctx.Value(key); id != nil {
+ ctx.bundleID = id.(string)
+ }
+ }
+ return ctx.bundleID
+ case ptransformKey:
+ if ctx.ptransformID == "" {
+ if id := ctx.Value(key); id != nil {
+ ctx.ptransformID = id.(string)
+ }
+ }
+ return ctx.ptransformID
+ }
+ return ctx.Context.Value(key)
+}
+
// SetBundleID sets the id of the current Bundle.
func SetBundleID(ctx context.Context, id string) context.Context {
- return context.WithValue(ctx, bundleKey, id)
+ var ptransformID string
+ if bctx, ok := ctx.(*beamCtx); ok {
+ ptransformID = bctx.ptransformID
+ }
+ return &beamCtx{Context: ctx, bundleID: id, ptransformID: ptransformID}
Review comment:
I considered that but then metrics following an emit would be incorrect,
short of retaining the parent PTransform ID and re-adding that, which would
work, but would be cumbersome. That approach is a viable alternative to caching
the Context in pardo.go though as it accomplishes the same goal.
Do you prefer that approach?
eg. re: correctness issue on ordering of event if the context isn't
re-allocated:
SDK sets PtransformID
SDK calls User ParDo
User ParDo1 emits - > SDK runs child ParDos which set their own PTransformIDs
User ParDo1 logs a metric -> Metric is associated with the wrong PTransform.
That is, we'd need to extract and re-assert the parent's PTransform ID
before returning from the ParDo process elements.
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Issue Time Tracking
-------------------
Worklog Id: (was: 121964)
Time Spent: 2h 10m (was: 2h)
> Reduce metrics overhead
> -----------------------
>
> Key: BEAM-4727
> URL: https://issues.apache.org/jira/browse/BEAM-4727
> Project: Beam
> Issue Type: Sub-task
> Components: sdk-go
> Reporter: Robert Burke
> Assignee: Robert Burke
> Priority: Major
> Time Spent: 2h 10m
> Remaining Estimate: 0h
>
> There are a few opportunities to avoid metrics overhead.
> First when setting state in the context, we allocate a new one for the stored
> value, per element. This generates a fair amount of objects for the garbage
> collector too. If we retain and re-use contexts within a bundle, we would
> have the opportunity to save on these costs.
> Also, it's possible that we have overhead on the metric updating paths. We
> can possibly do better than the general sync.Map, and avoid the type
> assertion cost for extracting values of known types from the maps.
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