Hi,
Why is this patch for 5.0 only?
On 2007-08-29 18:30 +0400, Konstantin Osipov Wrote：
> * kpettersson@stripped <kpettersson@stripped> [07/08/14 18:00]:
> >
> > ChangeSet@stripped, 2007-08-14 15:52:46+02:00, thek@adventure.(none) +1 -0
> > Bug #21074 Large query_cache freezes mysql server sporadically under heavy
> load
> >
> > Invaldating a subset of a sufficiently large query cache can take a long
> time.
> > During this time the server is efficiently frozen and no other operation can
> > be executed. This patch addresses this problem by setting a time limit on
> > how long time a dictionary access request can take before giving up on the
> > attempt. This patch does not work for query cache invalidations issued by
> > DROP, ALTER or RENAME TABLE operations.
> >
> > sql/sql_cache.cc@stripped, 2007-08-14 15:52:44+02:00, thek@adventure.(none) +27
> -1
> > Changed mutex locking to a timed spinn lock. If access to query cache
> dictionary
> > takes "a long time" (currently more than 0.1 seconds) the system fall backs
> on
> > ordinary statement execution.
>
> As discussed on IRC:
> since this patch is for 5.0 only, Shane/Sinisa should perform acceptance
> tests.
>
> After that, the patch is OK to push into 5.0 and null-merge into
> 5.1.
>
>
> Please see a minor comment below.
>
>
> > diff -Nrup a/sql/sql_cache.cc b/sql/sql_cache.cc
> > --- a/sql/sql_cache.cc 2007-05-10 14:54:53 +02:00
> > +++ b/sql/sql_cache.cc 2007-08-14 15:52:44 +02:00
> > @@ -1023,6 +1023,13 @@ Query_cache::send_result_to_client(THD *
> > Query_cache_block_table *block_table, *block_table_end;
> > ulong tot_length;
> > Query_cache_query_flags flags;
> > + const uint spin_treshold= 50000;
> > + const double lock_time_treshold= 0.1; /* Time in seconds */
> > + uint spin_count= 0;
> > + int lock_status= 0;
> > + ulong new_time= 0;
> > + ulong stop_time= 0;
> > +
> > DBUG_ENTER("Query_cache::send_result_to_client");
> >
> > /*
> > @@ -1069,7 +1076,26 @@ Query_cache::send_result_to_client(THD *
> > }
> > }
> >
> > - STRUCT_LOCK(&structure_guard_mutex);
> > + stop_time= my_clock()+(ulong)lock_time_treshold*CLOCKS_PER_SEC;
> > + while ((lock_status= pthread_mutex_trylock(&structure_guard_mutex)) ==
> EBUSY
> > + && spin_count < spin_treshold
> > + && new_time < stop_time)
>
> You don't have to keep track/check for both, new_time and
> spin_count - one of the parameters is enough.
> > + {
> > + spin_count++;
> > + if (spin_count%5)
> > + new_time= my_clock();
> > + pthread_yield();
> > + }
>
> You could use my_sleep instead of spinning - but that's to be
> decided based on Shane's tests.
>
> > + if (lock_status != 0)
> > + {
> > + /*
> > + Query cache is too busy doing something else.
> > + Fall back on ordinary statement execution.
> > + */
> > + DBUG_RETURN(0);
> > + }
>
> --
> -- Konstantin Osipov Software Developer, Moscow, Russia
> -- MySQL AB, www.mysql.com The best DATABASE COMPANY in the GALAXY
>
--
Turbolinux China
A: A12 Jianguomenwai Avenue Chaoyang District Beijing PRC
Z: 100022
E: hezx@stripped
T: 86-010-65054020-318
F: 86-010-65054017
