Elide bucket DB pruning scans when possible

Only do a (potentially expensive) pruning pass over the bucket DB
when the cluster state transition indicates that one or more nodes
are not in the same availability-state as the currently active state.

For instance, if a cluster state change is for a content node going
from Maintenance to Down, no pruning action is required since that
shall already have taken place during the processing of the initial
Down edge (and no buckets shall have been created for it in the meantime).

We do not currently attempt to elide distribution config changes, as
these happen much more rarely than cluster state changes.

1 files changed, 119 insertions, 0 deletions

diff --git a/storage/src/tests/distributor/bucket_db_prune_elision_test.cpp b/storage/src/tests/distributor/bucket_db_prune_elision_test.cpp
new file mode 100644
index 00000000000..4821d05a90c
--- /dev/null
+++ b/storage/src/tests/distributor/bucket_db_prune_elision_test.cpp
@@ -0,0 +1,119 @@
+// Copyright 2019 Oath Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+
+#include <vespa/storage/distributor/bucket_db_prune_elision.h>
+#include <vespa/vdslib/state/clusterstate.h>
+#include <gtest/gtest.h>
+
+using namespace ::testing;
+
+namespace storage::distributor {
+
+namespace {
+
+lib::ClusterState state_of(const char* str) {
+    return lib::ClusterState(str);
+}
+
+}
+
+TEST(IdempotentStateTransitionTest, state_differing_only_in_version_allows_elision) {
+    EXPECT_TRUE(db_pruning_may_be_elided(state_of("version:1 bits:8 distributor:3 storage:3"),
+                                         state_of("version:2 bits:8 distributor:3 storage:3")));
+}
+
+TEST(IdempotentStateTransitionTest, differing_cluster_state_disallows_elision) {
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("cluster:d distributor:3 storage:3"),
+                                          state_of("distributor:3 storage:3")));
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 storage:3"),
+                                          state_of("cluster:d distributor:3 storage:3")));
+}
+
+TEST(IdempotentStateTransitionTest, differing_distribution_bit_count_disallows_elision) {
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("bits:8 distributor:3 storage:3"),
+                                          state_of("bits:9 distributor:3 storage:3")));
+    // No explicit "bits:" implies 16 bits
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("bits:8 distributor:3 storage:3"),
+                                          state_of("distributor:3 storage:3")));
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 storage:3"),
+                                          state_of("bits:8 distributor:3 storage:3")));
+}
+
+TEST(IdempotentStateTransitionTest, same_implicit_distribution_bit_count_allows_elision) {
+    EXPECT_TRUE(db_pruning_may_be_elided(state_of("distributor:3 storage:3"),
+                                         state_of("bits:16 distributor:3 storage:3")));
+}
+
+TEST(IdempotentStateTransitionTest, changed_distributor_node_count_disallows_elision) {
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 storage:3"),
+                                          state_of("distributor:4 storage:3")));
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:4 storage:3"),
+                                          state_of("distributor:3 storage:3")));
+}
+
+TEST(IdempotentStateTransitionTest, changed_distributor_node_state_disallows_elision) {
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 .0.s:d storage:3"),
+                                          state_of("distributor:3 storage:3")));
+
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 storage:3"),
+                                          state_of("distributor:3 .0.s:d storage:3")));
+
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 .0.s:d storage:3"),
+                                          state_of("distributor:3 .0.s:u storage:3")));
+
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 .0.s:d storage:3"),
+                                          state_of("distributor:3 .1.s:d storage:3")));
+}
+
+TEST(IdempotentStateTransitionTest, changed_storage_node_count_disallows_elision) {
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 storage:3"),
+                                          state_of("distributor:3 storage:4")));
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 storage:4"),
+                                          state_of("distributor:3 storage:3")));
+}
+
+TEST(IdempotentStateTransitionTest, changed_storage_node_state_disallows_elision) {
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 storage:3 .0.s:d"),
+                                          state_of("distributor:3 storage:3")));
+
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 storage:3"),
+                                          state_of("distributor:3 storage:3 .0.s:d")));
+
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 storage:3 .0.s:d"),
+                                          state_of("distributor:3 storage:3 .0.s:u")));
+
+    EXPECT_FALSE(db_pruning_may_be_elided(state_of("distributor:3 storage:3 .0.s:d"),
+                                          state_of("distributor:3 storage:3 .1.s:d")));
+}
+
+TEST(IdempotentStateTransitionTest, may_elide_for_transition_between_different_effective_storage_down_states) {
+    // Maintenance -> Down edge shall already have pruned DB on Maintenance edge
+    EXPECT_TRUE(db_pruning_may_be_elided(state_of("distributor:3 storage:3 .0.s:m"),
+                                         state_of("distributor:3 storage:3 .0.s:d")));
+
+    // Down -> Maintenance edge shall already have pruned DB on Down edge
+    EXPECT_TRUE(db_pruning_may_be_elided(state_of("distributor:3 storage:3 .0.s:d"),
+                                         state_of("distributor:3 storage:3 .0.s:m")));
+}
+
+TEST(IdempotentStateTransitionTest, may_elide_for_transition_between_different_effective_storage_up_states) {
+    EXPECT_TRUE(db_pruning_may_be_elided(state_of("distributor:3 storage:3 .0.s:i"),
+                                         state_of("distributor:3 storage:3")));
+
+    EXPECT_TRUE(db_pruning_may_be_elided(state_of("distributor:3 storage:3 .1.s:r"),
+                                         state_of("distributor:3 storage:3")));
+    EXPECT_TRUE(db_pruning_may_be_elided(state_of("distributor:3 storage:3"),
+                                         state_of("distributor:3 storage:3 .2.s:r")));
+}
+
+// Changed startup timestamps imply that bucket info should be fetched from a node, but
+// does not imply that pruning is required.
+TEST(IdempotentStateTransitionTest, may_elide_changed_startup_timestamps) {
+    EXPECT_TRUE(db_pruning_may_be_elided(state_of("distributor:3 storage:3"),
+                                         state_of("distributor:3 storage:3 .0.t:123456")));
+    EXPECT_TRUE(db_pruning_may_be_elided(state_of("distributor:3 storage:3 .0.t:123456"),
+                                         state_of("distributor:3 storage:3")));
+    EXPECT_TRUE(db_pruning_may_be_elided(state_of("distributor:3 storage:3 .0.t:123456"),
+                                         state_of("distributor:3 storage:3 .0.t:654321")));
+}
+
+}