{
Context context = txn.getBaseDataset().getContext() ;
String mode = (null != context) ? (String) context.get(TDB.transactionJournalWriteBlockMode, "") : "" ;
if ("direct".equalsIgnoreCase(mode))
{
writeBlockBufferAllocator = new BufferAllocatorDirect() ;
}
else if ("mapped".equalsIgnoreCase(mode))
{
writeBlockBufferAllocator = new BufferAllocatorMapped(SystemTDB.BlockSize) ;
}