ingest/ledgerbackend: Create functional producer for BufferedStorageBackend

ingest/CHANGELOG.md

@@ -2,6 +2,12 @@
 
 All notable changes to this project will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org/).
 
+## Pending
+
+### New Features
+* Create new package `ingest/cdp` for new components which will assist towards writing data transformation pipelines as part of [Composable Data Platform](https://stellar.org/blog/developers/composable-data-platform). 
+* Add new functional producer, `cdp.PublishFromBufferedStorageBackend`. A new function which enables a private instance of `BufferedStorageBackend` to perfrom the role of a producer operator in streaming pipeline designs.  It will emit pre-computed `LedgerCloseMeta` from a chosen `DataStore`. The stream can use `PublishFromBufferedStorageBackend` as the origin of `LedgerCloseMeta`, providing a callback function which acts as the next operator in the stream, receiving the `LedgerCloseMeta`. [5462](https://github.com/stellar/go/pull/5462).
+
 ### Stellar Core Protocol 21 Configuration Update:
 * BucketlistDB is now the default database for stellar-core, replacing the experimental option. As a result, the `EXPERIMENTAL_BUCKETLIST_DB` configuration parameter has been deprecated.
 * A new mandatory parameter, `DEPRECATED_SQL_LEDGER_STATE`, has been added with a default value of false which equivalent to `EXPERIMENTAL_BUCKETLIST_DB` being set to true.

ingest/cdp/producer.go

@@ -0,0 +1,147 @@
+package cdp
+
+import (
+	"context"
+	"fmt"
+	"time"
+
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/stellar/go/ingest/ledgerbackend"
+	"github.com/stellar/go/support/datastore"
+	"github.com/stellar/go/support/log"
+	"github.com/stellar/go/support/ordered"
+	"github.com/stellar/go/xdr"
+)
+
+// provide testing hooks to inject mocks of these
+var datastoreFactory = datastore.NewDataStore
+
+// Generate a default buffered storage config with values
+// set to optimize buffered performance to some degree based
+// on number of ledgers per file expected in the underlying
+// datastore used by an instance of BufferedStorageBackend.
+//
+// these numbers were derived empirically from benchmarking analysis:
+// https://github.com/stellar/go/issues/5390
+//
+// ledgersPerFile - number of ledgers per file from remote datastore schema.
+// return - preconfigured instance of BufferedStorageBackendConfig
+func DefaultBufferedStorageBackendConfig(ledgersPerFile uint32) ledgerbackend.BufferedStorageBackendConfig {
+
+	config := ledgerbackend.BufferedStorageBackendConfig{
+		RetryLimit: 5,
+		RetryWait:  30 * time.Second,
+	}
+
+	switch {
+	case ledgersPerFile < 2:
+		config.BufferSize = 500
+		config.NumWorkers = 5
+		return config
+	case ledgersPerFile < 101:
+		config.BufferSize = 10
+		config.NumWorkers = 5
+		return config
+	default:
+		config.BufferSize = 10
+		config.NumWorkers = 2
+		return config
+	}
+}
+
+type PublisherConfig struct {
+	// Registry, optional, include to capture buffered storage backend metrics
+	Registry *prometheus.Registry
+	// RegistryNamespace, optional, include to emit buffered storage backend
+	// under this namespace
+	RegistryNamespace string
+	// BufferedStorageConfig, required
+	BufferedStorageConfig ledgerbackend.BufferedStorageBackendConfig
+	//DataStoreConfig, required
+	DataStoreConfig datastore.DataStoreConfig
+	// Log, optional, if nil uses go default logger
+	Log *log.Entry
+}
+
+// PublishFromBufferedStorageBackend - create an internal instance
+// of BufferedStorageBackend using provided config and emit
+// ledger metadata for the requested range by invoking the provided callback
+// once per ledger.
+//
+// The function is blocking, it will only return when a bounded range
+// is completed, the ctx is canceled, or an error occurs.
+//
+// ledgerRange - the requested range, can be bounded or unbounded.
+//
+// publisherConfig - PublisherConfig. Provide configuration settings for DataStore
+// and BufferedStorageBackend. Use DefaultBufferedStorageBackendConfig() to create
+// optimized BufferedStorageBackendConfig.
+//
+// ctx - the context. Caller uses this to cancel the internal ledger processing,
+// when canceled, the function will return asap with that error.
+//
+// callback - function. Invoked for every LedgerCloseMeta. If callback invocation
+// returns an error, the processing will stop and return an error asap.
+//
+// return - error, function only returns if requested range is bounded or an error occured.
+// nil will be returned only if bounded range requested and completed processing with no errors.
+// otherwise return will always be an error.
+func PublishFromBufferedStorageBackend(ledgerRange ledgerbackend.Range,
+	publisherConfig PublisherConfig,
+	ctx context.Context,
+	callback func(xdr.LedgerCloseMeta) error) error {
+
+	logger := publisherConfig.Log
+	if logger == nil {
+		logger = log.DefaultLogger
+	}
+
+	dataStore, err := datastoreFactory(ctx, publisherConfig.DataStoreConfig)
+	if err != nil {
+		return fmt.Errorf("failed to create datastore: %w", err)
+	}
+
+	var ledgerBackend ledgerbackend.LedgerBackend
+	ledgerBackend, err = ledgerbackend.NewBufferedStorageBackend(publisherConfig.BufferedStorageConfig, dataStore)
+	if err != nil {
+		return fmt.Errorf("failed to create buffered storage backend: %w", err)
+	}
+
+	if publisherConfig.Registry != nil {
+		ledgerBackend = ledgerbackend.WithMetrics(ledgerBackend, publisherConfig.Registry, publisherConfig.RegistryNamespace)
+	}
+
+	if ledgerRange.Bounded() && ledgerRange.To() <= ledgerRange.From() {
+		return fmt.Errorf("invalid end value for bounded range, must be greater than start")
+	}
+
+	if !ledgerRange.Bounded() && ledgerRange.To() > 0 {
+		return fmt.Errorf("invalid end value for unbounded range, must be zero")
+	}
+
+	from := ordered.Max(2, ledgerRange.From())
+	ledgerBackend.PrepareRange(ctx, ledgerRange)
+
+	for ledgerSeq := from; ledgerSeq <= ledgerRange.To() || !ledgerRange.Bounded(); ledgerSeq++ {
+		var ledgerCloseMeta xdr.LedgerCloseMeta
+
+		logger.WithField("sequence", ledgerSeq).Info("Requesting ledger from the backend...")
+		startTime := time.Now()
+		ledgerCloseMeta, err = ledgerBackend.GetLedger(ctx, ledgerSeq)
+
+		if err != nil {
+			return fmt.Errorf("error getting ledger, %w", err)
+		}
+
+		log.WithFields(log.F{
+			"sequence": ledgerSeq,
+			"duration": time.Since(startTime).Seconds(),
+		}).Info("Ledger returned from the backend")
+
+		err = callback(ledgerCloseMeta)
+		if err != nil {
+			return fmt.Errorf("received an error from callback invocation: %w", err)
+		}
+	}
+	return nil
+}