[tarantool-patches] Re: [PATCH 1/4] Fix races related to object outdating
Alex Khatskevich
avkhatskevich at tarantool.org
Wed Aug 1 20:44:00 MSK 2018
On 01.08.2018 15:36, Vladislav Shpilevoy wrote:
> Hi! Thanks for the patch! See 2 comments below.
>
>> diff --git a/vshard/router/init.lua b/vshard/router/init.lua
>> index 142ddb6..1a0ed2f 100644
>> --- a/vshard/router/init.lua
>> +++ b/vshard/router/init.lua
>> @@ -88,15 +94,18 @@ local function bucket_discovery(bucket_id)
>> log.verbose("Discovering bucket %d", bucket_id)
>> local last_err = nil
>> local unreachable_uuid = nil
>> - for uuid, replicaset in pairs(M.replicasets) do
>> - local _, err =
>> - replicaset:callrw('vshard.storage.bucket_stat',
>> {bucket_id})
>> - if err == nil then
>> - bucket_set(bucket_id, replicaset)
>> - return replicaset
>> - elseif err.code ~= lerror.code.WRONG_BUCKET then
>> - last_err = err
>> - unreachable_uuid = uuid
>> + for uuid, _ in pairs(M.replicasets) do
>> + -- Handle reload/reconfigure.
>> + replicaset = M.replicasets[uuid]
>
> 1. Please, explain, how is it possible, that before this line
> M.replicasets[uuid] can become nil. You iterate here over
> M.replicasets and on the previous line in '_' you have
> stored replicaset. How can here 'replicaset' differ from '_'?
>
> It has nothing in common with 'reload/reconfigure' case since
> you always iterate over M.replicasets - the most actual
> list of replicasets. Maybe you thought that pairs() stores
> its first argument into a temporary variable but looks like
> it is not. I checked it with a simple test:
>
> a = {}
> a.objs = {1, 2, 3, 4, 5}
> for k, v in pairs(a.objs) do
> print(a.objs[k])
> if k == 2 then
> a.objs = {6, 7, 8, 9, 10}
> end
> end
>
> Output:
> 1
> 2
> 8
> 9
> 10
> ---
> ...
Thanks. For some reason I was sure that pairs caches the table.
Fixed.
>> + if replicaset then
>> + local _, err =
>> + replicaset:callrw('vshard.storage.bucket_stat',
>> {bucket_id})
>> + if err == nil then
>> + return bucket_set(bucket_id, replicaset.uuid)
>> + elseif err.code ~= lerror.code.WRONG_BUCKET then
>> + last_err = err
>> + unreachable_uuid = uuid
>> + end
>> end
>> end
>> local err = nil
>> @@ -513,27 +522,28 @@ local function router_cfg(cfg)
>> end
>> box.cfg(box_cfg)
>> log.info("Box has been configured")
>> - M.connection_outdate_delay = cfg.connection_outdate_delay
>> - M.total_bucket_count = total_bucket_count
>> - M.collect_lua_garbage = collect_lua_garbage
>> - M.current_cfg = new_cfg
>> -- Move connections from an old configuration to a new one.
>> -- It must be done with no yields to prevent usage both of not
>> -- fully moved old replicasets, and not fully built new ones.
>> - lreplicaset.rebind_replicasets(new_replicasets, M.replicasets,
>> - M.connection_outdate_delay)
>> - M.replicasets = new_replicasets
>> + lreplicaset.rebind_replicasets(new_replicasets, M.replicasets)
>> -- Now the new replicasets are fully built. Can establish
>> -- connections and yield.
>> for _, replicaset in pairs(new_replicasets) do
>> replicaset:connect_all()
>> end
>> + lreplicaset.wait_masters_connect(new_replicasets)
>> + lreplicaset.outdate_replicasets(M.replicasets,
>> cfg.connection_outdate_delay)
>> + M.connection_outdate_delay = cfg.connection_outdate_delay
>> + M.total_bucket_count = total_bucket_count
>> + M.collect_lua_garbage = collect_lua_garbage
>> + M.current_cfg = cfg
>> + M.replicasets = new_replicasets
>> -- Update existing route map in-place.
>> - for bucket, rs in pairs(M.route_map) do
>> + local old_route_map = M.route_map
>> + M.route_map = {}
>> + for bucket, rs in pairs(old_route_map) do
>> M.route_map[bucket] = M.replicasets[rs.uuid]
>
> 2. Why do you need to save old_route_map into a
> separate variable? You can update M.route_map in place
> like it was done before. It is not? You fill the new
> route_map with exactly the same keys (maybe with different
> values, but it does not affect 'for' iteration). Moreover,
> when you create a new route_map instead of resetting the
> old, you double the memory. For huge bucket count it can
> be noticeable.
Yes there is no point in that change.
Fixed.
>> end
>> -
>> - lreplicaset.wait_masters_connect(new_replicasets)
>> if M.failover_fiber == nil then
>> lfiber.create(util.reloadable_fiber_f, M, 'failover_f',
>> 'Failover')
>> end
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