[mysql-dde] Re: Deadlock detection

  • From: "Fabricio Mota" <fabricio.oliveira@xxxxxxxxxxxxxxxx>
  • To: <mysql-dde@xxxxxxxxxxxxx>
  • Date: Wed, 8 Mar 2006 12:56:17 -0300

I find your idea interesting. I just call the attention to the question
"It detects the deadlock with a timeout of a transaction."

Notice that this couldn't be a common time out. This time out must consider 
verifying that the querie processor is waiting for a blocked resource.

At more, include it in documentation!


----- Original Message ----- 
From: "Peter Volk" <Peter.Volk@xxxxxxx>
To: <mysql-dde@xxxxxxxxxxxxx>
Sent: Wednesday, March 08, 2006 9:01 AM
Subject: [mysql-dde] Deadlock detection

> Hey,
> I've been spending some brains on the deadlock detection:
> In general there seem to be 2 ways of detecting a deadlock:
> 1) for every lock requested build a lock graph to detect cycles
> 2) If a dealock accors then build a lock graph to find the transaction
> involved with the lock and choose a transaction to roll back.
> The first solution is extramly complicated in a distributed system. So my
> proposal would be to use the second one. I found a paper on a method that
> sounds good (I'll send it to you as soon as I get home). It detects the
> deadlock with a timeout of a transaction. Once a transaction has past this
> timeout then a graph is build. To build this graph for a distributed 
> system
> you can query each server and ask it for their lockgraph. The idea is if a
> server suspects a deadlock then it starts to build the deadlock graph. 
> Each
> node is queried seperatly and the deadlock graph is build incrementell.
> After each increment the deadlock detection is performed on the graph. The
> atvantage of this instead of getting the graphs from all servers at once 
> and
> then building a big graph the incremental aproach can detect a deadlock
> earlier and without querying all server. if e.g. we have 3 servers and
> server 1 is in a deadlock with server 2. Server 1 suspects a deadlock. 
> After
> this it queries server 2 for its graph and then builds the deadlock graph
> locally. If the server already detects a deadlock with this smal subset of
> the global graph then the algorithm continues. If not then it queries the
> next server until the deadlock is found or the transaction is can continue
> (because the tablescan took so long). This method reduces the 
> communication
> between the Servers within the cluster since not always all servers are
> asked for their lock graph. Also it could be faster then always getting 
> the
> complete graph because the graph is smaller and the deadlock could be
> detected earlyer.
> What do you think?
> Peter
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