If you use a transactional storage engine in MySQL like InnoDB some of your transaction may be terminated by the storage engine because of deadlocks. Sadly it is a bit tricky to see what has led to the deadlock. SHOW ENGINE INNODB STATUS gives only a very minimal look into the state when it happened.

With the proxy and a little script we can track what happened in all open transactions before the deadlock happened. A classic example is the cross-over deadlock:

[36] received a ERR(1213, Deadlock found when trying to get lock; try restarting transaction), dumping all active transactions
  [35].1: select * from commit where id = 1 for update
  [35].2: select * from commit where id = 2 for update
  [36].1: select * from commit where id = 2 for update
  [36].2: select * from commit where id = 1 for update

35 and 36 are the two transactions we have open, the last statement in 36 triggered the deadlock.

In the script we stored all the statements per connection reset the statement stack as soon as a transaction is closed.


    print the statements of all transactions as soon as one of them aborted

    for now we know about:
    * Lock wait timeout exceeded
    * Deadlock found when trying to get lock


    if not proxy.global.trxs then
            proxy.global.trxs = { }

    function read_query(packet)
            if packet:byte() ~= proxy.COM_QUERY then return end

            if not proxy.global.trxs[proxy.connection.server.thread_id] then
                    proxy.global.trxs[proxy.connection.server.thread_id] = { }

            proxy.queries:append(1, packet)

            local t = proxy.global.trxs[proxy.connection.server.thread_id]

            t[#t + 1] = packet:sub(2)

            return proxy.PROXY_SEND_QUERY

    function read_query_result(inj)
            local res = inj.resultset
            local flags = res.flags

            if res.query_status == proxy.MYSQLD_PACKET_ERR then
                    local err_code     = res.raw:byte(2) + (res.raw:byte(3) * 256)
                    local err_sqlstate = res.raw:sub(5, 9)
                    local err_msg      = res.raw:sub(10)
                    -- print("-- error-packet: " .. err_code)

                    if err_code == 1205 or     -- Lock wait timeout exceeded
                       err_code == 1213 then   -- Deadlock found when trying to get lock
                            print(("[%d] received a ERR(%d, %s), dumping all active transactions"):format(

                            for thread_id, statements in pairs(proxy.global.trxs) do
                                    for stmt_id, statement in ipairs(statements) do
                                            print(("  [%d].%d: %s"):format(thread_id, stmt_id, statement))

            -- we are done, free the statement list
            if not flags.in_trans then
                    proxy.global.trxs[proxy.connection.server.thread_id] = nil

    function disconnect_client()
            proxy.global.trxs[proxy.connection.server.thread_id] = nil


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