driver: fix duplicate id error with mvvc on on take

Taking the minimum of the index is an implicit transactions, so it is
always done with 'read-confirmed' mvcc isolation level.
It can lead to errors when trying to make parallel 'take' calls with mvcc enabled.
It is hapenning because 'min' for several takes in parallel will be the same since
read confirmed isolation level makes visible all transactions that finished the commit.
To fix it we wrap it with box.begin/commit and set right isolation level.
Current fix does not resolve that bug in situations when we already are in transaction
since it will open nested transactions.

Part of #207

queue/abstract/driver/fifo.lua

@@ -97,7 +97,25 @@ end
 
 -- take task
 function method.take(self)
-    local task = self.space.index.status:min{state.READY}
+    local task
+    -- Taking the minimum is an implicit transactions, so it is
+    -- always done with 'read-confirmed' mvcc isolation level.
+    -- It can lead to errors when trying to make parallel 'take' calls with mvcc enabled.
+    -- It is hapenning because 'min' for several takes in parallel will be the same since
+    -- read confirmed isolation level makes visible all transactions that finished the commit.
+    -- To fix it we wrap it with box.begin/commit and set right isolation level.
+    -- Current fix does not resolve that bug in situations when we already are in transaction
+    -- since it will open nested transactions.
+    -- See https://github.com/tarantool/queue/issues/207
+    -- See https://www.tarantool.io/ru/doc/latest/concepts/atomic/txn_mode_mvcc/
+    if box.cfg.memtx_use_mvcc_engine and (not box.is_in_txn()) then
+        box.begin({txn_isolation = 'read-committed'})
+        task = self.space.index.status:min{state.READY}
+        box.commit()
+    else
+        task = self.space.index.status:min{state.READY}
+    end
+
     if task ~= nil and task[2] == state.READY then
         task = self.space:update(task[1], { { '=', 2, state.TAKEN } })
         self.on_task_change(task, 'take')

queue/abstract/driver/fifottl.lua

@@ -285,10 +285,21 @@ end
 -- take task
 function method.take(self)
     local task = nil
-    for _, t in self.space.index.status:pairs({state.READY}) do
-        if not is_expired(t) then
-            task = t
-            break
+    if box.cfg.memtx_use_mvcc_engine and (not box.is_in_txn()) then
+        box.begin({txn_isolation = 'read-committed'})
+        for _, t in self.space.index.status:pairs({state.READY}) do
+            if not is_expired(t) then
+                task = t
+                break
+            end
+        end
+        box.commit()
+    else
+        for _, t in self.space.index.status:pairs({state.READY}) do
+            if not is_expired(t) then
+                task = t
+                break
+            end
         end
     end
 

queue/abstract/driver/utube.lua

@@ -109,8 +109,25 @@ function method.take(self)
         if task[2] ~= state.READY then
             break
         end
+        local taken
+        -- Taking the minimum is an implicit transactions, so it is
+        -- always done with 'read-confirmed' mvcc isolation level.
+        -- It can lead to errors when trying to make parallel 'take' calls with mvcc enabled.
+        -- It is hapenning because 'min' for several takes in parallel will be the same since
+        -- read confirmed isolation level makes visible all transactions that finished the commit.
+        -- To fix it we wrap it with box.begin/commit and set right isolation level.
+        -- Current fix does not resolve that bug in situations when we already are in transaction
+        -- since it will open nested transactions.
+        -- See https://github.com/tarantool/queue/issues/207
+        -- See https://www.tarantool.io/ru/doc/latest/concepts/atomic/txn_mode_mvcc/
+        if box.cfg.memtx_use_mvcc_engine and (not box.is_in_txn()) then
+            box.begin({txn_isolation = 'read-committed'})
+            taken = self.space.index.utube:min{state.TAKEN, task[3]}
+            box.commit()
+        else
+            taken = self.space.index.utube:min{state.TAKEN, task[3]}
+        end
 
-        local taken = self.space.index.utube:min{state.TAKEN, task[3]}
         if taken == nil or taken[2] ~= state.TAKEN then
             task = self.space:update(task[1], { { '=', 2, state.TAKEN } })
             self.on_task_change(task, 'take')

queue/abstract/driver/utubettl.lua

@@ -300,7 +300,25 @@ function method.take(self)
             break
         elseif not is_expired(t) then
             local next_event = util.time() + t[i_ttr]
-            local taken = self.space.index.utube:min{state.TAKEN, t[i_utube]}
+            local taken
+            -- Taking the minimum is an implicit transactions, so it is
+            -- always done with 'read-confirmed' mvcc isolation level.
+            -- It can lead to errors when trying to make parallel 'take' calls with mvcc enabled.
+            -- It is hapenning because 'min' for several takes in parallel will be the same since
+            -- read confirmed isolation level makes visible all transactions that finished the commit.
+            -- To fix it we wrap it with box.begin/commit and set right isolation level.
+            -- Current fix does not resolve that bug in situations when we already are in transaction
+            -- since it will open nested transactions.
+            -- See https://github.com/tarantool/queue/issues/207
+            -- See https://www.tarantool.io/ru/doc/latest/concepts/atomic/txn_mode_mvcc/
+            if box.cfg.memtx_use_mvcc_engine and (not box.is_in_txn()) then
+                box.begin({txn_isolation = 'read-committed'})
+                taken = self.space.index.utube:min{state.TAKEN, t[i_utube]}
+                box.commit()
+            else
+                taken = self.space.index.utube:min{state.TAKEN, t[i_utube]}
+            end
+
             if taken == nil or taken[i_status] ~= state.TAKEN then
                 t = self.space:update(t[1], {
                     { '=', i_status, state.TAKEN },