[Monetdb-developers] [Monetdb-checkins] MonetDB5/src/modules/kernel unix.mx, , 1.24, 1.25

Martin Kersten Martin.Kersten at cwi.nl
Tue Jul 28 11:05:14 CEST 2009


Sjoerd Mullender wrote:
> Why do you want to be able to flush all changed files to disk?  MonetDB
Hint, we see very bad behavior in the second query, while it is identical
to the first. One idea is to 'somehow' kick the system into a state as
it was started. The assumption was that dirty pages may be polluting the memory,
so a forceful sync could do that.

"
        According  to  the  standard specification (e.g., POSIX.1-2001), sync()
        schedules the writes, but may return before the actual writing is done.
        However,  since  version  1.3.20 Linux does actually wait.  (This still
        does not guarantee data integrity: modern disks have large caches.) "
I was betting on the last remark

> already does flushes when they are needed for transaction support.  I
> don't think we need to tell the kernel to synchronize any other files
> with the disk.  This function doesn't do anything with memory management
> within the process.
> 
> Furthermore, this function is not available on Windows.
was to experiment with the blkjoin issues, it can be dropped again.
> 
> Martin Kersten wrote:
>> Update of /cvsroot/monetdb/MonetDB5/src/modules/kernel
>> In directory 23jxhf1.ch3.sourceforge.com:/tmp/cvs-serv20459
>>
>> Modified Files:
>> 	unix.mx 
>> Log Message:
>> We want to experiment with complete flushing memory in out of memory
>> queries.
>>
>>
>> U unix.mx
>> Index: unix.mx
>> ===================================================================
>> RCS file: /cvsroot/monetdb/MonetDB5/src/modules/kernel/unix.mx,v
>> retrieving revision 1.24
>> retrieving revision 1.25
>> diff -u -d -r1.24 -r1.25
>> --- unix.mx	7 Jan 2009 14:15:12 -0000	1.24
>> +++ unix.mx	27 Jul 2009 06:29:44 -0000	1.25
>> @@ -35,6 +35,10 @@
>>  address UNIXsetenv
>>  comment "Set the environment variable string.";
>>  
>> +command sync() :void 
>> +address UNIXsync
>> +comment "Flush memory, expensive but sometimes needed";
>> +
>>  @- Implementation
>>  The remainder is a straight forward mapping to the underlying
>>  facilities
>> @@ -113,4 +117,10 @@
>>  	return MAL_SUCCEED;
>>  }
>>  
>> +unix_export str UNIXsync(int *res);
>> +str UNIXsync(int *res){
>> +	(void) res;
>> +	sync();
>> +	return MAL_SUCCEED;
>> +}
>>  @}
>>
>>
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> 
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