driver: fix duplicate id error with mvvc on put and take

Taking the maximum or 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 'put' or 'take' calls with mvcc enabled.
It is hapenning because 'max' or 'min' for several puts 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

Author: better0fdead

queue/abstract/driver/fifo.lua

@@ -68,7 +68,27 @@ end
 
 -- put task in space
 function method.put(self, data, opts)
-    local max = self.space.index.task_id:max()
+    local max
+
+    -- Taking the maximum 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 'put' calls with mvcc enabled.
+    -- It is hapenning because 'max' for several puts 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'})
+        max = self.space.index.task_id:max()
+        box.commit()
+    else
+        max = self.space.index.task_id:max()
+    end
+
     local id = max and max[1] + 1 or 0
     local task = self.space:insert{id, state.READY, data}
     self.on_task_change(task, 'put')
@@ -77,7 +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

@@ -209,7 +209,27 @@ end
 
 -- put task in space
 function method.put(self, data, opts)
-    local max = self.space.index.task_id:max()
+    local max
+
+    -- Taking the maximum 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 'put' calls with mvcc enabled.
+    -- It is hapenning because 'max' for several puts 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'})
+        max = self.space.index.task_id:max()
+        box.commit()
+    else
+        max = self.space.index.task_id:max()
+    end
+
     local id = max and max[i_id] + 1 or 0
 
     local status
@@ -265,10 +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

@@ -75,7 +75,27 @@ end
 
 -- put task in space
 function method.put(self, data, opts)
-    local max = self.space.index.task_id:max()
+    local max
+
+    -- Taking the maximum 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 'put' calls with mvcc enabled.
+    -- It is hapenning because 'max' for several puts 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'})
+        max = self.space.index.task_id:max()
+        box.commit()
+    else
+        max = self.space.index.task_id:max()
+    end
+
     local id = max and max[1] + 1 or 0
     local task = self.space:insert{id, state.READY, tostring(opts.utube), data}
     self.on_task_change(task, 'put')
@@ -89,8 +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

@@ -217,7 +217,27 @@ end
 
 -- put task in space
 function method.put(self, data, opts)
-    local max = self.space.index.task_id:max()
+    local max
+
+    -- Taking the maximum 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 'put' calls with mvcc enabled.
+    -- It is hapenning because 'max' for several puts 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'})
+        max = self.space.index.task_id:max()
+        box.commit()
+    else
+        max = self.space.index.task_id:max()
+    end
+
     local id = max and max[i_id] + 1 or 0
 
     local status
@@ -280,7 +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 },

t/220-mvcc.t

@@ -0,0 +1,69 @@
+#!/usr/bin/env tarantool
+
+local qc = require('queue.compat')
+local log   = require('log')
+if not qc.check_version({2, 6, 1}) then
+    log.info('Tests skipped, tarantool version < 2.6.1')
+    return
+end
+
+local fiber = require('fiber')
+
+local test  = require('tap').test()
+test:plan(6)
+
+local queue = require('queue')
+
+local tnt   = require('t.tnt')
+tnt.cfg{memtx_use_mvcc_engine = true}
+
+local engine = 'memtx'
+
+test:ok(rawget(box, 'space'), 'box started')
+test:ok(queue, 'queue is loaded')
+
+local tube = queue.create_tube('test', 'fifo', { engine = engine, temporary = false})
+test:ok(tube, 'test tube created')
+test:is(tube.name, 'test', 'tube.name')
+test:is(tube.type, 'fifo', 'tube.type')
+
+--- That test checks that https://github.com/tarantool/queue/pull/211 is fixed.
+-- Previously trying to make parallel 'put' or 'take' calls failed with mvcc enabled.
+test:test('concurent put and take with mvcc', function(test)
+    test:plan(6)
+    -- channels are used to wait for fibers to finish
+    -- and check results of the 'take'/'put'.
+    local channel_put = fiber.channel(2)
+    test:ok(channel_put, 'channel created')
+    local channel_take = fiber.channel(2)
+    test:ok(channel_take, 'channel created')
+
+    for i = 1, 2 do
+        fiber.create(function(i)
+            local err = pcall(tube.put, tube, i)
+            channel_put:put(err)
+        end, i)
+    end
+
+    for i = 1, 2 do
+        local res = channel_put:get(1)
+        test:ok(res, 'task ' .. i .. ' was put')
+    end
+
+    for i = 1, 2 do
+        fiber.create(function(i)
+           local err = pcall(tube.take, tube)
+            channel_take:put(err)
+        end, i)
+    end
+
+    for i = 1, 2 do
+        local res = channel_take:get()
+        test:ok(res, 'task ' .. i .. ' was taken')
+    end
+end)
+
+tnt.finish()
+os.exit(test:check() and 0 or 1)
+
+-- vim: set ft=lua: