[Tarantool-patches] [PATCH vshard 1/1] storage: allow replica to boot before master

[Vladislav Shpilevoy <v.shpilevoy@tarantool.org>]

Before the patch a replica couldn't call vshard.storage.cfg()
before the master is bootstrapped. That could lead to an exception
in the middle of vshard.storage.cfg().

It sounds not so bad and even looks unreachable, because replica
bootstrap anyway is blocked in box.cfg() until a master node is
started, otherwise the replica instance is terminated.
But the box.cfg bootstrap != vshard bootstrap.

It could be that both replica and master nodes are already
bootstrapped and working, but vshard.storage.cfg() wasn't called
yet. In that case vshard.storage.cfg() on the replica wouldn't
block in box.cfg(), and would happily fail a few lines later in
vshard.storage.cfg() at attempt to touch not existing
box.space._bucket.

That was the case for cartridge. The framework configures
instances in its own way before vshard.storage.cfg(). Then it
calls vshard.storage.cfg() on them in arbitrary order, and
sometimes replicas were configured earlier than the master.

The fail is fixed by simply skipping the _bucket's trigger
installation on the replica node. Because so far it is not needed
here for anything. The trigger's sole purpose is to increment
bucket generation used only for DML on _bucket on the master node.

Now vshard.storage.cfg() on replica is able to finish before
master does the same. However the replica still won't be able to
handle vshard.storage.* requests until receives vshard schema
from master.

Closes #237
---
Branch: http://github.com/tarantool/vshard/tree/gerold103/gh-237-boot-replica-first
Issue: https://github.com/tarantool/vshard/issues/237

 test/lua_libs/storage_template.lua      |  55 +++++++++++-
 test/reload_evolution/storage.result    |  10 +++
 test/reload_evolution/storage.test.lua  |   8 ++
 test/router/boot_replica_first.result   | 112 ++++++++++++++++++++++++
 test/router/boot_replica_first.test.lua |  42 +++++++++
 vshard/storage/init.lua                 |  18 +++-
 vshard/storage/reload_evolution.lua     |  10 ++-
 7 files changed, 251 insertions(+), 4 deletions(-)
 create mode 100644 test/router/boot_replica_first.result
 create mode 100644 test/router/boot_replica_first.test.lua

diff --git a/test/lua_libs/storage_template.lua b/test/lua_libs/storage_template.lua
index 29a753d..84e4180 100644
--- a/test/lua_libs/storage_template.lua
+++ b/test/lua_libs/storage_template.lua
@@ -1,5 +1,7 @@
 #!/usr/bin/env tarantool
 
+local luri = require('uri')
+
 NAME = require('fio').basename(arg[0], '.lua')
 fiber = require('fiber')
 test_run = require('test_run').new()
@@ -10,12 +12,63 @@ log = require('log')
 if not cfg.shard_index then
     cfg.shard_index = 'bucket_id'
 end
+instance_uuid = util.name_to_uuid[NAME]
+
+--
+-- Bootstrap the instance exactly like vshard does. But don't
+-- initialize any vshard-specific code.
+--
+local function boot_like_vshard()
+    assert(type(box.cfg) == 'function')
+    for rs_uuid, rs in pairs(cfg.sharding) do
+        for replica_uuid, replica in pairs(rs.replicas) do
+            if replica_uuid == instance_uuid then
+                local box_cfg = {replication = {}}
+                box_cfg.instance_uuid = replica_uuid
+                box_cfg.replicaset_uuid = rs_uuid
+                box_cfg.listen = replica.uri
+                box_cfg.read_only = not replica.master
+                box_cfg.replication_connect_quorum = 0
+                box_cfg.replication_timeout = 0.1
+                for _, replica in pairs(rs.replicas) do
+                    table.insert(box_cfg.replication, replica.uri)
+                end
+                box.cfg(box_cfg)
+                if not replica.master then
+                    return
+                end
+                local uri = luri.parse(replica.uri)
+                box.schema.user.create(uri.login, {
+                    password = uri.password, if_not_exists = true,
+                })
+                box.schema.user.grant(uri.login, 'super')
+                return
+            end
+        end
+    end
+    assert(false)
+end
+
+local omit_cfg = false
+local i = 1
+while arg[i] ~= nil do
+    local key = arg[i]
+    i = i + 1
+    if key == 'boot_before_cfg' then
+        boot_like_vshard()
+        omit_cfg = true
+    end
+end
 
 vshard = require('vshard')
 echo_count = 0
 cfg.replication_connect_timeout = 3
 cfg.replication_timeout = 0.1
-vshard.storage.cfg(cfg, util.name_to_uuid[NAME])
+
+if not omit_cfg then
+    vshard.storage.cfg(cfg, instance_uuid)
+end
+
 function bootstrap_storage(engine)
     box.once("testapp:schema:1", function()
         if rawget(_G, 'CHANGE_SPACE_IDS') then
diff --git a/test/reload_evolution/storage.result b/test/reload_evolution/storage.result
index ebf4fdc..4652c4f 100644
--- a/test/reload_evolution/storage.result
+++ b/test/reload_evolution/storage.result
@@ -92,6 +92,16 @@ test_run:grep_log('storage_2_a', 'vshard.storage.reload_evolution: upgraded to')
 ...
 vshard.storage.internal.reload_version
 ---
+- 2
+...
+--
+-- gh-237: should be only one trigger. During gh-237 the trigger installation
+-- became conditional and therefore required to remember the current trigger
+-- somewhere. When reloaded from the old version, the trigger needed to be
+-- fetched from _bucket:on_replace().
+--
+#box.space._bucket:on_replace()
+---
 - 1
 ...
 -- Make sure storage operates well.
diff --git a/test/reload_evolution/storage.test.lua b/test/reload_evolution/storage.test.lua
index 56c1693..06f7117 100644
--- a/test/reload_evolution/storage.test.lua
+++ b/test/reload_evolution/storage.test.lua
@@ -37,6 +37,14 @@ package.loaded['vshard.storage'] = nil
 vshard.storage = require("vshard.storage")
 test_run:grep_log('storage_2_a', 'vshard.storage.reload_evolution: upgraded to') ~= nil
 vshard.storage.internal.reload_version
+--
+-- gh-237: should be only one trigger. During gh-237 the trigger installation
+-- became conditional and therefore required to remember the current trigger
+-- somewhere. When reloaded from the old version, the trigger needed to be
+-- fetched from _bucket:on_replace().
+--
+#box.space._bucket:on_replace()
+
 -- Make sure storage operates well.
 vshard.storage.bucket_force_drop(2000)
 vshard.storage.bucket_force_create(2000)
diff --git a/test/router/boot_replica_first.result b/test/router/boot_replica_first.result
new file mode 100644
index 0000000..1705230
--- /dev/null
+++ b/test/router/boot_replica_first.result
@@ -0,0 +1,112 @@
+-- test-run result file version 2
+test_run = require('test_run').new()
+ | ---
+ | ...
+REPLICASET_1 = { 'box_1_a', 'box_1_b', 'box_1_c' }
+ | ---
+ | ...
+test_run:create_cluster(REPLICASET_1, 'router', {args = 'boot_before_cfg'})
+ | ---
+ | ...
+util = require('util')
+ | ---
+ | ...
+util.wait_master(test_run, REPLICASET_1, 'box_1_a')
+ | ---
+ | ...
+_ = test_run:cmd("create server router with script='router/router_2.lua'")
+ | ---
+ | ...
+_ = test_run:cmd("start server router")
+ | ---
+ | ...
+
+--
+-- gh-237: replica should be able to boot before master. Before the issue was
+-- fixed, replica always tried to install a trigger on _bucket space even when
+-- it was not created on a master yet - that lead to an exception in
+-- storage.cfg. Now it should not install the trigger at all, because anyway it
+-- is not needed on replica for anything.
+--
+
+test_run:switch('box_1_b')
+ | ---
+ | - true
+ | ...
+vshard.storage.cfg(cfg, instance_uuid)
+ | ---
+ | ...
+-- _bucket is not created yet. Will fail.
+util.check_error(vshard.storage.call, 1, 'read', 'echo', {100})
+ | ---
+ | - attempt to index field '_bucket' (a nil value)
+ | ...
+
+test_run:switch('default')
+ | ---
+ | - true
+ | ...
+util.map_evals(test_run, {REPLICASET_1}, 'bootstrap_storage(\'memtx\')')
+ | ---
+ | ...
+
+test_run:switch('box_1_a')
+ | ---
+ | - true
+ | ...
+vshard.storage.cfg(cfg, instance_uuid)
+ | ---
+ | ...
+
+test_run:switch('box_1_b')
+ | ---
+ | - true
+ | ...
+test_run:wait_lsn('box_1_b', 'box_1_a')
+ | ---
+ | ...
+-- Fails, but gracefully. Because the bucket is not found here.
+vshard.storage.call(1, 'read', 'echo', {100})
+ | ---
+ | - null
+ | - bucket_id: 1
+ |   reason: Not found
+ |   code: 1
+ |   type: ShardingError
+ |   message: 'Cannot perform action with bucket 1, reason: Not found'
+ |   name: WRONG_BUCKET
+ | ...
+-- Should not have triggers.
+#box.space._bucket:on_replace()
+ | ---
+ | - 0
+ | ...
+
+test_run:switch('router')
+ | ---
+ | - true
+ | ...
+vshard.router.bootstrap()
+ | ---
+ | - true
+ | ...
+vshard.router.callro(1, 'echo', {100})
+ | ---
+ | - 100
+ | ...
+
+test_run:switch("default")
+ | ---
+ | - true
+ | ...
+test_run:cmd('stop server router')
+ | ---
+ | - true
+ | ...
+test_run:cmd('delete server router')
+ | ---
+ | - true
+ | ...
+test_run:drop_cluster(REPLICASET_1)
+ | ---
+ | ...
diff --git a/test/router/boot_replica_first.test.lua b/test/router/boot_replica_first.test.lua
new file mode 100644
index 0000000..7b1b3fd
--- /dev/null
+++ b/test/router/boot_replica_first.test.lua
@@ -0,0 +1,42 @@
+test_run = require('test_run').new()
+REPLICASET_1 = { 'box_1_a', 'box_1_b', 'box_1_c' }
+test_run:create_cluster(REPLICASET_1, 'router', {args = 'boot_before_cfg'})
+util = require('util')
+util.wait_master(test_run, REPLICASET_1, 'box_1_a')
+_ = test_run:cmd("create server router with script='router/router_2.lua'")
+_ = test_run:cmd("start server router")
+
+--
+-- gh-237: replica should be able to boot before master. Before the issue was
+-- fixed, replica always tried to install a trigger on _bucket space even when
+-- it was not created on a master yet - that lead to an exception in
+-- storage.cfg. Now it should not install the trigger at all, because anyway it
+-- is not needed on replica for anything.
+--
+
+test_run:switch('box_1_b')
+vshard.storage.cfg(cfg, instance_uuid)
+-- _bucket is not created yet. Will fail.
+util.check_error(vshard.storage.call, 1, 'read', 'echo', {100})
+
+test_run:switch('default')
+util.map_evals(test_run, {REPLICASET_1}, 'bootstrap_storage(\'memtx\')')
+
+test_run:switch('box_1_a')
+vshard.storage.cfg(cfg, instance_uuid)
+
+test_run:switch('box_1_b')
+test_run:wait_lsn('box_1_b', 'box_1_a')
+-- Fails, but gracefully. Because the bucket is not found here.
+vshard.storage.call(1, 'read', 'echo', {100})
+-- Should not have triggers.
+#box.space._bucket:on_replace()
+
+test_run:switch('router')
+vshard.router.bootstrap()
+vshard.router.callro(1, 'echo', {100})
+
+test_run:switch("default")
+test_run:cmd('stop server router')
+test_run:cmd('delete server router')
+test_run:drop_cluster(REPLICASET_1)
diff --git a/vshard/storage/init.lua b/vshard/storage/init.lua
index c6a78fe..ed577f9 100644
--- a/vshard/storage/init.lua
+++ b/vshard/storage/init.lua
@@ -94,6 +94,17 @@ if not M then
         -- detect that _bucket was not changed between yields.
         --
         bucket_generation = 0,
+        --
+        -- Reference to the function used as on_replace trigger on
+        -- _bucket space. It is used to replace the trigger with
+        -- a new function when reload happens. It is kept
+        -- explicitly because the old function is deleted on
+        -- reload from the global namespace. On the other hand, it
+        -- is still stored in _bucket:on_replace() somewhere, but
+        -- it is not known where. The only 100% way to be able to
+        -- replace the old function is to keep its reference.
+        --
+        bucket_on_replace = nil,
 
         ------------------- Garbage collection -------------------
         -- Fiber to remove garbage buckets data.
@@ -2435,8 +2446,11 @@ local function storage_cfg(cfg, this_replica_uuid, is_reload)
     local uri = luri.parse(this_replica.uri)
     schema_upgrade(is_master, uri.login, uri.password)
 
-    local old_trigger = box.space._bucket:on_replace()[1]
-    box.space._bucket:on_replace(bucket_generation_increment, old_trigger)
+    if is_master then
+        local old_trigger = M.bucket_on_replace
+        box.space._bucket:on_replace(bucket_generation_increment, old_trigger)
+        M.bucket_on_replace = bucket_generation_increment
+    end
 
     lreplicaset.rebind_replicasets(new_replicasets, M.replicasets)
     lreplicaset.outdate_replicasets(M.replicasets)
diff --git a/vshard/storage/reload_evolution.lua b/vshard/storage/reload_evolution.lua
index 5d09b11..f38af74 100644
--- a/vshard/storage/reload_evolution.lua
+++ b/vshard/storage/reload_evolution.lua
@@ -17,6 +17,14 @@ migrations[#migrations + 1] = function(M)
     -- Code to update Lua objects.
 end
 
+migrations[#migrations + 1] = function(M)
+    local bucket = box.space._bucket
+    if bucket then
+        assert(M.bucket_on_replace == nil)
+        M.bucket_on_replace = bucket:on_replace()[1]
+    end
+end
+
 --
 -- Perform an update based on a version stored in `M` (internals).
 -- @param M Old module internals which should be updated.
@@ -33,7 +41,7 @@ local function upgrade(M)
         log.error(err_msg)
         error(err_msg)
     end
-    for i = start_version, #migrations  do
+    for i = start_version + 1, #migrations do
         local ok, err = pcall(migrations[i], M)
         if ok then
             log.info('vshard.storage.reload_evolution: upgraded to %d version',
-- 
2.21.1 (Apple Git-122.3)