From: Hiromichi Watari Date: November 19 2011 2:23am Subject: Re: Concurrent table access from InnoDB List-Archive: http://lists.mysql.com/internals/38393 Message-Id: <1321669391.73426.YahooMailNeo@web121508.mail.ne1.yahoo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable Hi Shawn and Rick,=0AThank you for your response.=0AMy question was whether= a client thread can access more than one table at a time in the course of = join execution (parallel access of multiple tables) to speed up the query i= f an extra slave thread is available.=0AI do not know if there is anything = in InnoDB (or storage engine in general) which serializes access to tables = preventing parallel access.=0A=0AHiromichi=0A=0A=0A________________________= ________=0AFrom: Shawn Green (MySQL) =0ATo: Rick = James =0ACc: internals@stripped =0ASent: Frid= ay, November 18, 2011 5:16 PM=0ASubject: Re: Concurrent table access from I= nnoDB=0A=0AOn 11/18/2011 16:29, Rick James wrote:=0A> Is this what keeps th= ere from being parallelism in PARTITIONed tables?=0A> =0A> ...=0A=0ANo. Tho= se partitions are accessed internally. Multiple threads can be spawned in t= he context of resolving a single query. Any lack of parallelism in resolvin= g PARTITIONed table queries is simply a matter of design time and effort.= =0A=0ANow, in the context of accessing internal resources any query that re= quires a JOIN will need to touch at least two tables under the same user co= ntext.=A0 Perhaps I misunderstood the original question?=0A=0A> =0A> Hi,=0A= > Is it possible for a client connection thread to access 2 tables concurre= ntly from InnoDB, say using a slave thread ?=A0 Or is access limited to one= table at a time per client connection thread ?=0A=0APerhaps he was asking = about the optimizer processing a command that needed to touch two or more t= ables?=A0 If that's the purpose of the question then of course more than on= e table can be accessed in the context of a single connection. This happens= very frequently.=A0 I cannot say with absolute certainty if those tables a= re processed in parallel but I would be concerned if they were not.=0A=0AI = was reading his question more like this: Can the same connection be used to= open multiple queries where each query is pointing to a separate table? In= that context, each connection can only have one active command.=0A=0A-- Sh= awn Green=0AMySQL Principal Technical Support Engineer=0AOracle USA, Inc. -= Hardware and Software, Engineered to Work Together.=0AOffice: Blountville,= TN=0A=0A-- MySQL Internals Mailing List=0AFor list archives: http://lists.= mysql.com/internals=0ATo unsubscribe:=A0 =A0 http://lists.mysql.com/interna= ls?unsub=3Dhiromichiwatari@stripped