Please refer the code:
org.apache.cassandra.db.ColumnFamilyStore
public String getFlushPath()
{
long guessedSize = 2 * DatabaseDescriptor.getMemtableThroughput() *
1024*1024; // 2* adds room for keys, column indexes
String location =
DatabaseDescriptor.getDataFileLocationForTable(table_, guessedSize);
if (location == null)
throw new RuntimeException("Insufficient disk space to flush");
return new File(location,
getTempSSTableFileName()).getAbsolutePath();
}
and we can go through org.apache.cassandra.config.DatabaseDescriptor:
public static String getDataFileLocationForTable(String table, long
expectedCompactedFileSize)
{
long maxFreeDisk = 0;
int maxDiskIndex = 0;
String dataFileDirectory = null;
String[] dataDirectoryForTable =
getAllDataFileLocationsForTable(table);
for ( int i = 0 ; i < dataDirectoryForTable.length ; i++ )
{
File f = new File(dataDirectoryForTable[i]);
if( maxFreeDisk < f.getUsableSpace())
{
maxFreeDisk = f.getUsableSpace();
maxDiskIndex = i;
}
}
// Load factor of 0.9 we do not want to use the entire disk that is
too risky.
maxFreeDisk = (long)(0.9 * maxFreeDisk);
if( expectedCompactedFileSize < maxFreeDisk )
{
dataFileDirectory = dataDirectoryForTable[maxDiskIndex];
currentIndex = (maxDiskIndex + 1 )%dataDirectoryForTable.length ;
}
else
{
currentIndex = maxDiskIndex;
}
return dataFileDirectory;
}
So, DataFileDirectories means multiple disks or disk-partitions.
I think your storage01, storage02 and storage03 are in same disk or disk
partition.
2010/4/26 Roland Hänel <[email protected]>
> I have a configuration like this:
>
> <DataFileDirectories>
> <DataFileDirectory>/storage01/cassandra/data</DataFileDirectory>
> <DataFileDirectory>/storage02/cassandra/data</DataFileDirectory>
> <DataFileDirectory>/storage03/cassandra/data</DataFileDirectory>
> </DataFileDirectories>
>
> After loading a big chunk of data into cassandra, I end up wich some 70GB
> in the first directory, and only about 10GB in the second and third one. All
> rows are quite small, so it's not just some big rows that contain the
> majority of data.
>
> Does Cassandra have the ability to 'see' the maximum available space in
> these directory? I'm asking myself this question since my limit is 100GB,
> and the first directory is approaching this limit...
>
> And, wouldn't it be better if Cassandra tried to 'load-balance' the files
> inside the directories because this will result in better (read) performance
> if the directories are on different disks (which is the case for me)?
>
> Any help is appreciated.
>
> Roland
>
>
