Thank you,  Rahul!
From: Rahul Singh <>
Sent: Saturday, April 21, 2018 3:02:11 PM
Subject: Re: copy from one table to another

That’s correct.

On Apr 21, 2018, 5:05 AM -0400, Kyrylo Lebediev <>, 

You mean that correct table UUID should be specified as suffix in directory 
For example:


cqlsh> select id from system_schema.tables where keyspace_name='test' and 


Directory name:




From: Rahul Singh <>
Sent: Thursday, April 19, 2018 10:53:11 PM
Subject: Re: copy from one table to another

Each table has a different Guid — doing a hard link may work as long as the 
sstable dir’s guid is he same as the newly created table in the system schema.

Rahul Singh

Anant Corporation

On Apr 19, 2018, 10:41 AM -0500, Kyrylo Lebediev <>, 

The table is too large to be copied fast/effectively , so I'd like to leverage 
immutableness  property of SSTables.

My idea is to:

1) create new empty table (NewTable) with the same structure as existing one 
2) at some time run simultaneous 'nodetool snapshot -t ttt <keyspace> OldTable' 
on all nodes -- this will create point in time state of OldTable

3) on each node run:
       for each file in OldTable ttt snapshot directory:


     nodetool refresh <keyspace> NewTable

4) nodetool repair NewTable
5) Use OldTable and NewTable independently (Read/Write)

Are there any issues with using hardlinks (ln) instead of copying (cp) in this 



From: Rahul Singh <>
Sent: Wednesday, April 18, 2018 2:07:17 AM
Subject: Re: copy from one table to another

1. Make a new table with the same schema.
For each node
2. Shutdown node
3. Copy data from Source sstable dir to new sstable dir.

This will do what you want.

Rahul Singh

Anant Corporation

On Apr 16, 2018, 4:21 PM -0500, Kyrylo Lebediev <>, 
Thanks,  Ali.
I just need to copy a large table in production without actual copying by using 
hardlinks. After this both tables should be used independently (RW). Is this a 
supported way or not?

From: Ali Hubail <>
Sent: Monday, April 16, 2018 6:51:51 PM
Subject: Re: copy from one table to another

If you want to copy a portion of the data to another table, you can also use 
sstable cql writer. It is more of an advanced feature and can be tricky, but 
once you write the new sstables, you can then use the sstableloader to stream 
the new data into the new table.
check this out:

I have recently used this to clean up 500 GB worth of sstable data in order to 
purge tombstones that were mistakenly generated by the client.
obviously this is not as fast as hardlinks + refresh, but it's much faster and 
more efficient than using cql to copy data accross the tables.
take advantage of CQLSSTableWriter.builder.sorted() if you can, and utilize 
writetime if you have to.

Ali Hubail

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Kyrylo Lebediev <>

04/16/2018 10:37 AM

Please respond to

        "" <>,

        Re: copy from one table to another

Any issues if we:

1) create an new empty table with the same structure as the old one
2) create hardlinks ("ln without -s"): 
.../<newtable>-<newuuid>/<newkeyspacename>-<newtable>-* ---> 
3) run nodetool refresh -- newkeyspacename newtable

and then query/modify both tables independently/simultaneously?

In theory, as SSTables are immutable, this should work, but could there be some 
hidden issues?



From: Dmitry Saprykin <>
Sent: Sunday, April 8, 2018 7:33:03 PM
Subject: Re: copy from one table to another

You can copy hardlinks to ALL SSTables from old to new table and then delete 
part of data you do not need in a new one.

On Sun, Apr 8, 2018 at 10:20 AM, Nitan Kainth 
<<>> wrote:
If it for testing and you don’t need any specific data, just copy a set of 
sstables with all files of that sequence and move to target tables directory 
and rename it.

Restart target node or run nodetool refresh

Sent from my iPhone

On Apr 8, 2018, at 4:15 AM, onmstester onmstester 
<<>> wrote:

Is there any way to copy some part of a table to another table in cassandra? A 
large amount of data should be copied so i don't want to fetch data to client 
and stream it back to cassandra using cql.

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