From 9801d0ae40536285eada0dc95f801eff9b643872 Mon Sep 17 00:00:00 2001
From: dawn <dawn@tangled.org>
Date: Thu, 22 Oct 2026 02:32:51 +0300
Subject: [PATCH] spindle/db: keep idle db connections open so bursts don't
 churn them

Signed-off-by: dawn <dawn@tangled.org>
---
 spindle/db/db.go           |  4 +++
 spindle/db/fd_leak_test.go | 64 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 68 insertions(+)
 create mode 100644 spindle/db/fd_leak_test.go

diff --git a/spindle/db/db.go b/spindle/db/db.go
index 12643f4cf..453122c55 100644
--- a/spindle/db/db.go
+++ b/spindle/db/db.go
@@ -45,6 +45,8 @@ func queryDIDs(q DBTX, query string, args ...any) ([]syntax.DID, error) {
 	return out, rows.Err()
 }
 
+const maxIdleConns = 64
+
 func Make(ctx context.Context, dbPath string) (*DB, error) {
 	logger := log.FromContext(ctx)
 	logger = log.SubLogger(logger, "db")
@@ -53,6 +55,8 @@ func Make(ctx context.Context, dbPath string) (*DB, error) {
 	if err != nil {
 		return nil, err
 	}
+	// viewers that cancel mid-query would churn fds, so keep the idle conns around
+	db.SetMaxIdleConns(maxIdleConns)
 
 	conn, err := db.Conn(ctx)
 	if err != nil {
diff --git a/spindle/db/fd_leak_test.go b/spindle/db/fd_leak_test.go
new file mode 100644
index 000000000..078ee30cb
--- /dev/null
+++ b/spindle/db/fd_leak_test.go
@@ -0,0 +1,64 @@
+package db
+
+import (
+	"context"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync"
+	"testing"
+	"time"
+)
+
+func fdsOnFile(t *testing.T, path string) int {
+	t.Helper()
+	entries, err := os.ReadDir("/proc/self/fd")
+	if err != nil {
+		t.Skip("no /proc/self/fd here")
+	}
+	n := 0
+	for _, e := range entries {
+		if target, err := os.Readlink(filepath.Join("/proc/self/fd", e.Name())); err == nil && target == path {
+			n++
+		}
+	}
+	return n
+}
+
+func TestClosedConnectionsReleaseTheirDescriptors(t *testing.T) {
+	ctx := context.Background()
+	path := filepath.Join(t.TempDir(), "spindle.db")
+	database, err := Make(ctx, path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	t.Cleanup(func() { database.Close() })
+
+	var wg sync.WaitGroup
+	for i := range 30 {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			queryCtx, cancel := context.WithTimeout(ctx, 20*time.Millisecond)
+			defer cancel()
+			if i%2 == 0 {
+				var n int
+				_ = database.QueryRowContext(queryCtx, `
+					with recursive c(x) as (select 1 union all select x + 1 from c where x < 5000000)
+					select count(*) from c`).Scan(&n)
+				return
+			}
+			rows, err := database.QueryContext(queryCtx, `select name from sqlite_master`)
+			if err == nil {
+				rows.Close()
+			}
+		}()
+	}
+	wg.Wait()
+	time.Sleep(200 * time.Millisecond)
+
+	open := database.Stats().OpenConnections
+	if fds := fdsOnFile(t, strings.TrimSpace(path)); fds > open+1 {
+		t.Fatalf("%d descriptors on the db file with %d open connections, closed connections keep theirs", fds, open)
+	}
+}
-- 
2.54.0