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From:Christian Mack Date:May 18 1999 3:10pm
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Paul DuBois wrote:
> At 11:01 AM -0800 1/6/2000, Michael Palm wrote:
> >[I am very new to mysql so I hope this ins't too silly}:
> >
> >The documentation for insert and update says:
> >
> >"if you specify the keyword LOW_PRIORITY, execution of the (insert or
> >update)
> >is delayed until no other clients are reading from the table".
> >
> >However, if I submit a select which takes a long time, any insert or
> >updare
> >on a queried table seems to wait until the select has completed or been
> >killed,
> >even without using LOW_PRIORITY. Am I doing something wrong here?
> No.  INSERT operations always have to wait for SELECT operations
> if the SELECT is in progress at the time that the INSERT is issued.
> The difference between using and not using LOW_PRIORITY is this:
> If you don't use LOW_PRIORITY, the INSERT will block SELECT statements
> that are issued after the INSERT.  So if a SELECT is in progress,
> the INSERT will block until the SELECT finishes.  Then the INSERT is
> done.  Then the other SELECTs are done.
> With LOW_PRIORITY, if a SELECT is in progress, the INSERT blocks until
> the SELECT finishes.  If no more SELECTs have come in in the meantime,
> the INSERT proceeds.  However, if other SELECTs have come in and are
> pending by the time the initial SELECT finishes, those SELECTs take
> priority over the INSERT, even though the INSERT arrived earlier.
> The INSERT is executed only when no other SELECTs are pending.
> (This is what the manual means when is says that "the insert is delayed
> until no other clients are reading from the table.)
> That's my understanding of it, anyway.  If that's wrong, someone please
> correct me.
> --
> Paul DuBois, paul@stripped

Hi Paul

You are absolutely right.

You only forgot to mention, that when other INSERTs arrive while the first INSERT is
waiting, then the two INSERTs are merged together in one multi INSERT, which usually is
faster than the two originally issued INSERTs are.


  • Re: INSERT, SELECT and LOW_PRIORITYPaul DuBois18 May
    • Re: INSERT, SELECT and LOW_PRIORITYChristian Mack18 May