On Sun, Apr 18, 2010 at 11:14, dir dir <sikerasa...@gmail.com> wrote: > Hi Gary, > >>The main reason is that the compaction operation (removing deleted >>values) currently requires that an entire row be read into memory. > > Thank you for your explanation. But I still do not understand what do you > mean. >
When you delete a column in cassandra, the data is not really deleted. Instead a flag is turned on indicating the column is no longer valid (we call it a 'tombstone'). During compaction the column family is scanned and the tombstones are truly deleted. > in my opinion, Actually the row contents must fit in available memory. > if row contents are not fit in available memory, our software will raise > exception out of memory. since it is true( "the row contents must fit in > available memory"), > then why you said that is a problem which it (Cassandra) cannot solved?? > It was not correct of me to say it is a problem that cassandra cannot solve. Memory-efficient compactions will be addressed. > You say: "compaction operation requires that entire row be read into memory" > whether this is a problem of "out of memory"?? When we need to perform > compaction operation?? In what situation we shall perform compaction > operation?? You will need to address the large rows yourself (consider breaking them up). You can identify these rows during compaction by setting RowWarningThresholdInMB in storage-conf.xml. When a big enough row comes along, it is logged so you can go back later and address the problem. Regards, Gary. > Thank You. > > Dir. >
