iskakaushik commented on code in PR #252:
URL: https://github.com/apache/iceberg-go/pull/252#discussion_r1913861589


##########
table/scanner.go:
##########
@@ -259,129 +286,119 @@ func matchDeletesToData(entry iceberg.ManifestEntry, 
positionalDeletes []iceberg
        return out, nil
 }
 
-func (scan *Scan) PlanFiles(ctx context.Context) ([]FileScanTask, error) {
+// fetchPartitionSpecFilteredManifests retrieves the table's current snapshot,
+// fetches its manifest files, and applies partition-spec filters to remove 
irrelevant manifests.
+func (scan *Scan) fetchPartitionSpecFilteredManifests() 
([]iceberg.ManifestFile, error) {
        snap := scan.Snapshot()
        if snap == nil {
                return nil, nil
        }
 
-       // step 1: filter manifests using partition summaries
-       // the filter depends on the partition spec used to write the manifest 
file
-       // so create a cache of filters for each spec id
-       manifestEvaluators := 
newKeyDefaultMapWrapErr(scan.buildManifestEvaluator)
+       // Fetch all manifests for the current snapshot.
        manifestList, err := snap.Manifests(scan.io)
        if err != nil {
                return nil, err
        }
 
-       // remove any manifests that we don't need to use
+       // Build per-spec manifest evaluators and filter out irrelevant 
manifests.
+       manifestEvaluators := 
newKeyDefaultMapWrapErr(scan.buildManifestEvaluator)
        manifestList = slices.DeleteFunc(manifestList, func(mf 
iceberg.ManifestFile) bool {
                eval := manifestEvaluators.Get(int(mf.PartitionSpecID()))
                use, err := eval(mf)
                return !use || err != nil
        })
 
-       // step 2: filter the data files in each manifest
-       // this filter depends on the partition spec used to write the manifest 
file
-       partitionEvaluators := newKeyDefaultMap(scan.buildPartitionEvaluator)
+       return manifestList, nil
+}
+
+// collectManifestEntries concurrently opens manifests, applies partition and 
metrics
+// filters, and accumulates both data entries and positional-delete entries.
+func (scan *Scan) collectManifestEntries(
+       ctx context.Context,
+       manifestList []iceberg.ManifestFile,
+) (*manifestEntries, error) {
        metricsEval, err := newInclusiveMetricsEvaluator(
-               scan.metadata.CurrentSchema(), scan.rowFilter, 
scan.caseSensitive, scan.options["include_empty_files"] == "true")
+               scan.metadata.CurrentSchema(),
+               scan.rowFilter,
+               scan.caseSensitive,
+               scan.options["include_empty_files"] == "true",
+       )
        if err != nil {
                return nil, err
        }
 
        minSeqNum := minSequenceNum(manifestList)
-       dataEntries := make([]iceberg.ManifestEntry, 0)
-       positionalDeleteEntries := make([]iceberg.ManifestEntry, 0)
-
-       nworkers := min(scan.concurrency, len(manifestList))
-       var wg sync.WaitGroup
-
-       manifestChan := make(chan iceberg.ManifestFile, len(manifestList))
-       entryChan := make(chan []iceberg.ManifestEntry, 20)
-
-       ctx, cancel := context.WithCancelCause(ctx)
-       for i := 0; i < nworkers; i++ {
-               wg.Add(1)
-
-               go func() {
-                       defer wg.Done()
-
-                       for {
-                               select {
-                               case m, ok := <-manifestChan:
-                                       if !ok {
-                                               return
-                                       }
-
-                                       if !scan.checkSequenceNumber(minSeqNum, 
m) {
-                                               continue
-                                       }
-
-                                       entries, err := openManifest(scan.io, m,
-                                               
partitionEvaluators.Get(int(m.PartitionSpecID())), metricsEval)
-                                       if err != nil {
-                                               cancel(err)
-                                               break
-                                       }
-
-                                       entryChan <- entries
-                               case <-ctx.Done():
-                                       return
-                               }
-                       }
-               }()
-       }
+       concurrencyLimit := min(scan.concurrency, len(manifestList))
 
-       go func() {
-               wg.Wait()
-               close(entryChan)
-       }()
+       entries := newManifestEntries()
+       g, _ := errgroup.WithContext(ctx)
+       g.SetLimit(concurrencyLimit)
 
-       for _, m := range manifestList {
-               manifestChan <- m
-       }
-       close(manifestChan)
-
-Loop:
-       for {
-               select {
-               case <-ctx.Done():
-                       return nil, context.Cause(ctx)
-               case entries, ok := <-entryChan:
-                       if !ok {
-                               // closed!
-                               break Loop
+       partitionEvaluators := newKeyDefaultMap(scan.buildPartitionEvaluator)
+
+       for _, mf := range manifestList {
+               if !scan.checkSequenceNumber(minSeqNum, mf) {
+                       continue
+               }
+
+               g.Go(func() error {
+                       partEval := 
partitionEvaluators.Get(int(mf.PartitionSpecID()))
+                       manifestEntries, err := openManifest(scan.io, mf, 
partEval, metricsEval)
+                       if err != nil {
+                               return err
                        }
 
-                       for _, e := range entries {
+                       for _, e := range manifestEntries {
                                df := e.DataFile()
                                switch df.ContentType() {
                                case iceberg.EntryContentData:
-                                       dataEntries = append(dataEntries, e)
+                                       entries.addDataEntry(e)
                                case iceberg.EntryContentPosDeletes:
-                                       positionalDeleteEntries = 
append(positionalDeleteEntries, e)
+                                       entries.addPositionalDeleteEntry(e)
                                case iceberg.EntryContentEqDeletes:
-                                       return nil, fmt.Errorf("iceberg-go does 
not yet support equality deletes")
+                                       return fmt.Errorf("iceberg-go does not 
yet support equality deletes")
                                default:
-                                       return nil, fmt.Errorf("%w: unknown 
DataFileContent type (%s): %s",
+                                       return fmt.Errorf("%w: unknown 
DataFileContent type (%s): %s",
                                                ErrInvalidMetadata, 
df.ContentType(), e)
                                }
                        }
-               }
+                       return nil
+               })
+       }

Review Comment:
   No, mostly simplified code. For context I am working on adding a couple more 
scanners and trying to build an abstraction that would make it easy.



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