Hi, I have some questions related to the SSTable in the Cassandra, as I am
doing a project to use it and hope someone in this list can share some thoughts.
My understand is the SSTable is per column family. But each column family could
have multi SSTable files. During the runtime, one row COULD split into more
than one SSTable file, even this is not good for performance, but it does
happen, and Cassandra will try to merge and store one row data into one SSTable
file during compassion.
The question is when one row is split in multi SSTable files, what is the
boundary? Or let me ask this way, if one row exists in 2 SSTable files, if I
run sstable2json tool to run on both SSTable files individually:
1) I will expect same row key could show up in both sstable2json output, as
this one row exists in both SSTable files, right?2) If so, what is the
boundary? Will Cassandra guarantee the column level as the boundary? What I
mean is that for one column's data, it will be guaranteed to be either in the
first file, or 2nd file, right? There is no chance that Cassandra will cut the
data of one column into 2 part, and one part stored in first SSTable file, and
the other part stored in second SSTable file. Is my understanding correct?3) If
what we are talking about are only the SSTable files in snapshot, incremental
backup SSTable files, exclude the runtime SSTable files, will anything change?
For snapshot or incremental backup SSTable files, first can one row data still
may exist in more than one SSTable file? And any boundary change in this
case?4) If I want to use incremental backup SSTable files as the way to catch
data being changed, is it a good way to do what I try to archive? In this case,
what happen in the following example:
For column family A:at Time 0, one row key (key1) has some data. It is being
stored and back up in SSTable file 1.at Time 1, if any column for key1 has any
change (a new column insert, a column updated/deleted, or even whole row being
deleted), I will expect this whole row exists in the any incremental backup
SSTable files after time 1, right?
What happen if the above row just happen to store in more than one SSTable
file?at Time 0, one row key (key1) has some data, and it just is stored in
SSTable file1 and file2, and being backup.at Time 1, if one column is added in
row key1, and the change in fact will happen in SSTable file2 only in this
case, and if we do a incremental backup after that, what SSTable files should I
expect in this backup? Both SSTable files? Or Just SSTable file 2?
I was thinking incremental backup SSTable files are good candidate for catching
data being changed, but as one row data could exist in multi SSTable file makes
thing complex now. Did anyone have any experience to use SSTable file in this
way? What are the lessons?
Thanks
Yong
