I use dsbulk for text based backup and restore of cassandra cluster. I have created a python script that backsup/restores the all the tables in cassandra cluster using dsbulk load/unload but it takes long time even for less data due to new session created for each table (approx 7s), In my case I have 70 tables, so 70*7s is added due to session creation. Is there a way to backup data from all tables in a cluster using a single session using dsbulk? From the docs, I see dsbulk is suitable only for single table load/unload at a time. Is there any alternative or other approach for this? Please suggest if any..!
Thanks..
No, there isn't a way to load/unload multiple tables in a single DSBulk execution because it doesn't make sense to do so.
In any case, using unloading data to CSV isn't recommended as a means of backing up your cluster because there are no guarantees that the data will be consistent at a point in time.
The correct way of backing up a Cassandra cluster is using the nodetool snapshot command. For details, see Apache Cassandra Backups.
If you're interested, there is an open-source tool which allows you to automate backups -- https://github.com/thelastpickle/cassandra-medusa. Cheers!
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I searched through the internet a lot and saw a lot of ways to backup and restore a Cassandra cluster, such as nodetool snapshot and Medusa. but my question is that can I use dsbulk to backup a Cassandra cluster. What are its limitations? Why doesn't anyone suggest that?
It's possible to use it in some cases, but it's not practical because (that are primary, list could be bigger):
DSBulk put an additional load onto the cluster nodes because it's going through the standard read path. In contrast to that nodetool snapshot just create a hardlinks to the files with data, no additional load to the nodes
It's harder to implement incremental backups with DSBulk - you need to come with condition for SELECT that will find only data that changed since the last backup, so you need to have timestamp column, because you can't do the WHERE condition on the value of writetime function. Plus it will require rescanning of whole data anyway. Plus it's impossible to find what data were deleted. With nodetool snapshot, you just compare what files has changed since last backup, and backup only them.
I am very new to Cassandra and any help here would be appreciated. I have a cluster of 6 nodes that spans 2 datacenters (3 nodes to each cluster). My client has decided that they do not want to renew their Cassandra license with Datastax anymore and want their data exported into a format that can be easily imported into another Database in the future. I was thinking of exporting the data as a CSV file, but since the data is distributed between all the nodes, I am not sure what is the best way to export all the data.
One option - You should be able to use the CQL COPY command - which copies the data into a CSV format. The nice thing about copy is that you can run it from a single node (i.e. it is not a "node" level tool). Command would be (once in cqlsh):
CQL> COPY . to '/path/to/file'
If there is a LOT of data, or a lot of tables, this tool may not be a great fit. But for small number of tables that don't have HUGE rowcounts (< several million), this works well. Hope that helps.
-Jim
Since 2018 you can use DSBulk with DSE to export or import data to/from CSV (by default), or JSON. Since the end of 2019 it's possible to use it with open source Cassandra as well.
It could be as simple as:
dsbulk unload -k keyspace -t table -u user -p password -url filename
DSBulk is heavily optimized for fast data export, without putting too much load onto the coordinator node that happens when you just run select * from table.
You can control what columns to export, and even provide your own query, etc. DataStax blog has a series of blog posts about different aspects of using DSBulk:
Introduction and Loading
More Loading
Common Settings
Unloading
Counting
Examples for Loading From Other Locations
You can use CQL COPY command for exporting the data from Cassandra cluster. However it is performant for small set of data if you are having big size of data this command is not useful cause it will give some error or timeout issue. Also, you may use sstabledump and export your node-wise date into JSON format. Hope, this will useful for you.
I have implemented small script for this purpose. It isn't the best way, since it slow and, in my experience, produces connection errors on system tables. But it could be useful for inspecting Cassandra on small datasets: https://github.com/kirillt/cassandra-utils
I have to change the schema of one of my tables in Cassandra. It's cannot be done by simply using ALTER TABLE command, because there are some changes in primary key.
So the question is: How to do such a migration in the best way?
Using COPY command in cql is not an option in here because dump file can be really huge.
Can I solve this problem by not creating some custom application?
Like Guillaume has suggested in the comment - you can't do this directly in cassandra. Schema altering operations are very limited here. You have to perform such migration manually using one of suggested there tools OR if you have very large tables you can leverage Spark.
Spark can efficiently read data from your nodes, transform them locally and save them back to db. Remember that such migration requires reading whole db content, so might take a while. It might be the most performant solution, however needs some bigger preparation - Spark cluster setup.
I have a cassandra cluster with multiple data centres. I want to archive data monthly and purge that data. There are numerous articles of backing up and restoring but not where its mentioned to archive data in cassandra cluster.
Can someone please let me know how can I archive my data in cassandra cluster monthly and purge the data.
I think there is no such tool that can be used for archive cassandra.You have to write either Spark Jobs or map reduce job that use CqlInputFormat to archive the data.You can follow below links that help you to understand how people are archiving data in cassandra:
[1] - [http://docs.wso2.org/display/BAM240/Archive+Cassandra+Data]
[2] - http://docs.wso2.org/pages/viewpage.action?pageId=32345660
[3] - http://accelconf.web.cern.ch/AccelConf/ICALEPCS2013/papers/tuppc004.pdf
There is also a way using which you can turn on incremental backup in cassandra which can be used like CDC.
It is the best practice to use timewindow compaction strategy and set the window of monthly on your tables along with TTL(month), so that data older than a month can be purged.
If you write a purge job that does this work of deletion (on tables which do not have correct compaction strategy applied) then this can impact the cluster performance because searching the data on date/month basic will overwhelm the cluster.
I have experienced this, where we ultimately have to go back changing the structure of tables and altered the compaction strategy. That is why having the table design right at the first place is very important. We need to think about (in the beginning itself) not only how the data will be inserted and read in tables but also how it will be deleted and then frame the keys, compaction, ttl, etc.
For archiving just write a few lines of code to read data from Cassandra and put it to you archival location.
Let me know if this help in getting the end result you want or if you have further question that I can help with.
I'm looking for a tool to load CSV into Cassandra. I was hoping to use RazorSQL for this but I've been told that it will be several months out.
What is a good tool?
Thanks
1) If you have all the data to be loaded in place you can try sstableloader(only for cassandra 0.8.x onwards) utility to bulk load the data.For more details see:cassandra bulk loader
2) Cassandra has introduced BulkOutputFormat bulk loading data into cassandra with hadoop job in latest version that is cassandra-1.1.x onwards.
For more details see:Bulkloading to Cassandra with Hadoop
I'm dubious that tool support would help a great deal with this, since a Cassandra schema needs to reflect the queries that you want to run, rather than just being a generic model of your domain.
The built-in bulk loading mechanism for cassandra is via BinaryMemtables: http://wiki.apache.org/cassandra/BinaryMemtable
However, whether you use this or the more usual Thrift interface, you still probably need to manually design a mapping from your CSV into Cassandra ColumnFamilies, taking into account the queries you need to run. A generic mapping from CSV-> Cassandra may not be appropriate since secondary indexes and denormalisation are commonly needed.
For Cassandra 1.1.3 and higher, there is the CQL COPY command that is available for importing (or exporting) data to (or from) a table. According to the documentation, if you are importing less than 2 million rows, roughly, then this is a good option. Is is much easier to use than the sstableloader and less error prone. The sstableloader requires you to create strictly formatted .db files whereas the CQL COPY command accepts a delimited text file. Documenation here:
http://www.datastax.com/docs/1.1/references/cql/COPY
For larger data sets, you should use the sstableloader.http://www.datastax.com/docs/1.1/references/bulkloader. A working example is described here http://www.datastax.com/dev/blog/bulk-loading.