Re: bzr commit into mysql-6.0-falcon-team branch (vvaintroub:2970) Bug#35255

[Kevin Lewis]

Vlad,  Looks good, OK to push.  Great job!

Vladislav Vaintroub wrote:
> #At file:///G:/bzr/bug35255/
> 
>  2970 Vladislav Vaintroub	2009-01-15
>        Bug#35255 : test falcon_bug_22165 fails sporadically.
>       
>       Problem : Crashes happen in a concurrent workload with inserts/create
> table/drop table, or insert/alter table.
>       
>       The reason for assertions is a race condition in Dbb::findSection() function,
> that is calledon the first insert() after table is created ot altered.
>       When 2 threads are looking for the same section  in Dbb::sections hashtable at
> the very same time and do not find it , they will  insert 2 equal entries into the table.
> One entry will be deleted, when table is dropped. Another entry will stay and will with
> high probability become invalid  when section for this table is reused (invalid means root
> page does not match sectionId).  In this case, next access to section will fail with an
> assert.
>       
>       The fix is to synchronize access to the Dbb::section hashtable with a mutex
> .There are very few  calls to Dbb::findSection in normal case, so synchronization will not
> introduce performance losses.
> modified:
>   storage/falcon/Dbb.cpp
>   storage/falcon/Dbb.h
> 
> === modified file 'storage/falcon/Dbb.cpp'
> --- a/storage/falcon/Dbb.cpp	2008-12-19 18:45:32 +0000
> +++ b/storage/falcon/Dbb.cpp	2009-01-15 09:23:38 +0000
> @@ -374,6 +374,8 @@ Section* Dbb::findSection(int32 sectionI
>  	int slot = sectionId % SECTION_HASH_SIZE;
>  	Section *section;
>  
> +	Sync sync (&sectionsMutex, "Dbb::findSection");
> +	sync.lock(Exclusive);
>  	for (section = sections [slot]; section; section = section->hash)
>  		if (section->sectionId == sectionId)
>  			return section;
> @@ -625,7 +627,10 @@ void Dbb::deleteSection(int32 sectionId,
>  		Section::deleteSection (this, sectionId, transId);
>  
>  	Section *section;
> -	
> +
> +	Sync sync(&sectionsMutex, "Dbb::deleteSection");
> +	sync.lock(Exclusive);
> +
>  	for (Section **ptr = sections + slot; (section = *ptr); ptr =
> &section->hash)
>  		if (section->sectionId == sectionId)
>  			{
> 
> === modified file 'storage/falcon/Dbb.h'
> --- a/storage/falcon/Dbb.h	2008-12-19 18:45:32 +0000
> +++ b/storage/falcon/Dbb.h	2009-01-15 09:23:38 +0000
> @@ -29,6 +29,7 @@
>  #include "PageType.h"
>  #include "SyncObject.h"
>  #include "SparseArray.h"
> +#include "Mutex.h"
>  
>  #define TRANSACTION_ID(transaction)		((transaction) ? transaction->transactionId
> : 0)
>  
> @@ -200,6 +201,7 @@ public:
>  	bool		utf8;
>  	bool		noLog;
>  	Section		**sections;
> +	Mutex		sectionsMutex;
>  	int			debug;
>  	int			sequence;
>  	int			odsVersion;
> 
>