make the new 'spack load' faster (#14628)

before, a 'time spack load singularity'
4.129u 0.346s 0:04.47 99.7%	0+0k 0+8io 0pf+0w

after, a 'time spack load singularity'
0.844u 0.319s 0:01.16 99.1%	0+0k 0+16io 0pf+0w

1 files changed, 13 insertions, 10 deletions

diff --git a/lib/spack/spack/cmd/load.py b/lib/spack/spack/cmd/load.py
index 80c7263a7a..09f3fd31ee 100644
--- a/lib/spack/spack/cmd/load.py
+++ b/lib/spack/spack/cmd/load.py
@@ -12,6 +12,7 @@ import spack.cmd.common.arguments as arguments
 import spack.environment as ev
 import spack.util.environment
 import spack.user_environment as uenv
+import spack.store
 
 description = "add package to the user environment"
 section = "user environment"
@@ -63,15 +64,17 @@ def load(parser, args):
         tty.msg(*msg)
         return 1
 
-    if 'dependencies' in args.things_to_load:
-        include_roots = 'package' in args.things_to_load
-        specs = [dep for spec in specs
-                 for dep in spec.traverse(root=include_roots, order='post')]
+    with spack.store.db.read_transaction():
+        if 'dependencies' in args.things_to_load:
+            include_roots = 'package' in args.things_to_load
+            specs = [dep for spec in specs
+                     for dep in
+                     spec.traverse(root=include_roots, order='post')]
 
-    env_mod = spack.util.environment.EnvironmentModifications()
-    for spec in specs:
-        env_mod.extend(uenv.environment_modifications_for_spec(spec))
-        env_mod.prepend_path(uenv.spack_loaded_hashes_var, spec.dag_hash())
-    cmds = env_mod.shell_modifications(args.shell)
+        env_mod = spack.util.environment.EnvironmentModifications()
+        for spec in specs:
+            env_mod.extend(uenv.environment_modifications_for_spec(spec))
+            env_mod.prepend_path(uenv.spack_loaded_hashes_var, spec.dag_hash())
+        cmds = env_mod.shell_modifications(args.shell)
 
-    sys.stdout.write(cmds)
+        sys.stdout.write(cmds)