From 4ce75ecc78b4b5ab21d7cf2f043679518a4fbceb Mon Sep 17 00:00:00 2001
From: fiatjaf <fiatjaf@gmail.com>
Date: Tue, 16 Apr 2024 17:11:39 -0300
Subject: [PATCH] limit index scans to the maximum of total returnable events.

---
 badger/query.go | 25 ++++++++++++++++++-------
 bolt/query.go   | 19 +++++++++++++------
 lmdb/query.go   | 19 +++++++++++++------
 3 files changed, 44 insertions(+), 19 deletions(-)

diff --git a/badger/query.go b/badger/query.go
index 9618233..eaf2e74 100644
--- a/badger/query.go
+++ b/badger/query.go
@@ -34,12 +34,21 @@ func (b BadgerBackend) QueryEvents(ctx context.Context, filter nostr.Filter) (ch
 		return nil, err
 	}
 
+	// max number of events we'll return
+	limit := b.MaxLimit / 4
+	if filter.Limit > 0 && filter.Limit < b.MaxLimit {
+		limit = filter.Limit
+	}
+
 	go func() {
 		defer close(ch)
 
 		// actually iterate
 		for _, q := range queries {
 			q := q
+
+			pulled := 0 // this query will be hardcapped at this global limit
+
 			go b.View(func(txn *badger.Txn) error {
 				// iterate only through keys and in reverse order
 				opts := badger.IteratorOptions{
@@ -87,7 +96,15 @@ func (b BadgerBackend) QueryEvents(ctx context.Context, filter nostr.Filter) (ch
 
 						// check if this matches the other filters that were not part of the index
 						if extraFilter == nil || extraFilter.Matches(evt) {
-							q.results <- evt
+							select {
+							case q.results <- evt:
+								pulled++
+								if pulled > limit {
+									break
+								}
+							case <-ctx.Done():
+								break
+							}
 						}
 
 						return nil
@@ -98,12 +115,6 @@ func (b BadgerBackend) QueryEvents(ctx context.Context, filter nostr.Filter) (ch
 			})
 		}
 
-		// max number of events we'll return
-		limit := b.MaxLimit
-		if filter.Limit > 0 && filter.Limit < limit {
-			limit = filter.Limit
-		}
-
 		// receive results and ensure we only return the most recent ones always
 		emittedEvents := 0
 
diff --git a/bolt/query.go b/bolt/query.go
index e30985c..dc657ca 100644
--- a/bolt/query.go
+++ b/bolt/query.go
@@ -34,12 +34,21 @@ func (b *BoltBackend) QueryEvents(ctx context.Context, filter nostr.Filter) (cha
 		return nil, err
 	}
 
+	// max number of events we'll return
+	limit := b.MaxLimit / 4
+	if filter.Limit > 0 && filter.Limit < b.MaxLimit {
+		limit = filter.Limit
+	}
+
 	ch := make(chan *nostr.Event)
 	go func() {
 		defer close(ch)
 
 		for _, q := range queries {
 			q := q
+
+			pulled := 0 // this query will be hardcapped at this global limit
+
 			go b.db.View(func(txn *bolt.Tx) error {
 				defer close(q.results)
 
@@ -76,6 +85,10 @@ func (b *BoltBackend) QueryEvents(ctx context.Context, filter nostr.Filter) (cha
 					if extraFilter == nil || extraFilter.Matches(evt) {
 						select {
 						case q.results <- evt:
+							pulled++
+							if pulled > limit {
+								break
+							}
 						case <-ctx.Done():
 							break
 						}
@@ -85,12 +98,6 @@ func (b *BoltBackend) QueryEvents(ctx context.Context, filter nostr.Filter) (cha
 			})
 		}
 
-		// max number of events we'll return
-		limit := b.MaxLimit
-		if filter.Limit > 0 && filter.Limit < limit {
-			limit = filter.Limit
-		}
-
 		// receive results and ensure we only return the most recent ones always
 		emittedEvents := 0
 
diff --git a/lmdb/query.go b/lmdb/query.go
index c02ebea..aacd3f3 100644
--- a/lmdb/query.go
+++ b/lmdb/query.go
@@ -35,12 +35,21 @@ func (b *LMDBBackend) QueryEvents(ctx context.Context, filter nostr.Filter) (cha
 		return nil, err
 	}
 
+	// max number of events we'll return
+	limit := b.MaxLimit / 4
+	if filter.Limit > 0 && filter.Limit < b.MaxLimit {
+		limit = filter.Limit
+	}
+
 	ch := make(chan *nostr.Event)
 	go func() {
 		defer close(ch)
 
 		for _, q := range queries {
 			q := q
+
+			pulled := 0 // this will be hard-capped at the global limit of the query
+
 			go b.lmdbEnv.View(func(txn *lmdb.Txn) error {
 				txn.RawRead = true
 				defer close(q.results)
@@ -105,6 +114,10 @@ func (b *LMDBBackend) QueryEvents(ctx context.Context, filter nostr.Filter) (cha
 					if extraFilter == nil || extraFilter.Matches(evt) {
 						select {
 						case q.results <- evt:
+							pulled++
+							if pulled >= limit {
+								break
+							}
 						case <-ctx.Done():
 							break
 						}
@@ -120,12 +133,6 @@ func (b *LMDBBackend) QueryEvents(ctx context.Context, filter nostr.Filter) (cha
 			log.Printf("lmdb: error on cursor iteration: %v\n", err)
 		}
 
-		// max number of events we'll return
-		limit := b.MaxLimit
-		if filter.Limit > 0 && filter.Limit < limit {
-			limit = filter.Limit
-		}
-
 		// receive results and ensure we only return the most recent ones always
 		emittedEvents := 0