From bc8381613d4caab185089394d9df4bd7deb11934 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Thu, 6 Aug 2020 19:17:51 +0300
Subject: [PATCH] app/vmselect: reduce memory allocations by pre-allocatin
 memory for time series map and for a list of time series names

---
 app/vmselect/netstorage/netstorage.go | 6 +++---
 lib/storage/search.go                 | 7 +++++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/app/vmselect/netstorage/netstorage.go b/app/vmselect/netstorage/netstorage.go
index 8491722b38..56ef994c64 100644
--- a/app/vmselect/netstorage/netstorage.go
+++ b/app/vmselect/netstorage/netstorage.go
@@ -594,10 +594,10 @@ func ProcessSearchQuery(sq *storage.SearchQuery, fetchData bool, deadline Deadli
 	defer vmstorage.WG.Done()
 
 	sr := getStorageSearch()
-	sr.Init(vmstorage.Storage, tfss, tr, *maxMetricsPerSearch, deadline.deadline)
+	maxSeriesCount := sr.Init(vmstorage.Storage, tfss, tr, *maxMetricsPerSearch, deadline.deadline)
 
-	m := make(map[string][]storage.BlockRef)
-	var orderedMetricNames []string
+	m := make(map[string][]storage.BlockRef, maxSeriesCount)
+	orderedMetricNames := make([]string, 0, maxSeriesCount)
 	blocksRead := 0
 	for sr.NextMetricBlock() {
 		blocksRead++
diff --git a/lib/storage/search.go b/lib/storage/search.go
index a8cb32f9a6..ce723149d9 100644
--- a/lib/storage/search.go
+++ b/lib/storage/search.go
@@ -90,7 +90,9 @@ func (s *Search) reset() {
 // Init initializes s from the given storage, tfss and tr.
 //
 // MustClose must be called when the search is done.
-func (s *Search) Init(storage *Storage, tfss []*TagFilters, tr TimeRange, maxMetrics int, deadline uint64) {
+//
+// Init returns the upper bound on the number of found time series.
+func (s *Search) Init(storage *Storage, tfss []*TagFilters, tr TimeRange, maxMetrics int, deadline uint64) int {
 	if s.needClosing {
 		logger.Panicf("BUG: missing MustClose call before the next call to Init")
 	}
@@ -110,10 +112,11 @@ func (s *Search) Init(storage *Storage, tfss []*TagFilters, tr TimeRange, maxMet
 
 	if err != nil {
 		s.err = err
-		return
+		return 0
 	}
 
 	s.storage = storage
+	return len(tsids)
 }
 
 // MustClose closes the Search.