Rules for migration from Cassandra 3.x to Scylla

[Ilya Shibaev]

Hello!
Several questions  about migration data from  Cassandra 3.x to Scylla (current version 2.0.2).
1. is it supported? documentation cover Scylla 1.7... its too old...

2. migration from Cassandra  to Scylla available only if each clusters have the same amount of nodes or  its possible to have difference in host count?

3. after snapshot at Cassandra side, how to copy the sstable files from the Apache Cassandra cluster to a local folder on the intermediate node? create dedicated folder per each Cassandra  node or put all data into one folder for whole cluster?

4. how to run Scylla sstableloader - set one (and the same) scylla destination host for each Cassandra source host, or set scylla's destination host list?

5. where is the log file of sstableloader utility?

[Tomer Sandler]

Hi Ilya,

1. Yes, it is supported - please review our Cassandra to Scylla migration process document. This document also answers questions 3 and 4.

Scylla 2.0.X schema is still not fully compatible with Cassandra 3.x schema, so the limitations and know issues still apply.

2. Possible to have difference host count, but you need to make sure you meet your keyspace/s replication factor setting and make sure you have sufficient storage space.

5. sstableloader prints the output on screen. You can send the output to a log file if you wish. You can use -v flag for verbose output

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ScyllaDB

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[Ilya Shibaev]

Thank you, Tomer!
 but I saw documnetation about q3 and q4.
May be I'm not correct, but -
About q3 I found only this at point 4 -
"Option 1 (recommended): copy the sstable files from the Apache Cassandra cluster to a local folder on the intermediate node." - does it mean one folder at intermediate node for whole cluster data? I wasn't sure...

About q4 I found at point 7 -
"We recommend running several sstableloaders in parallel and utilizing all Scylla nodes as targets for sstable loading. Start with one keyspace and its underlying sstable files from all Apache Cassandra nodes. After completion, continue to the next keyspace and so on."
Does it mean configuration, where, from intermediate node, we run one Scylla sstableloader task per each Cassandra keyspace, AND every task will have one Scylla destination host per each task?

Sorry, I wasn't sure, am I understand it correctly or not. I prefer ask before, than after

[Ilya Shibaev]

and about question 5 -
I think then, it's necessary to create another topic, because I tried 'v' flag, but there are no messages... There are no bad result, no data in scylla...

[Tomer Sandler]

See inline.

On Wed, Jan 24, 2018 at 5:01 PM, Ilya Shibaev <ishi...@gmail.com> wrote:

Thank you, Tomer!
 but I saw documnetation about q3 and q4.
May be I'm not correct, but -
About q3 I found only this at point 4 -
"Option 1 (recommended): copy the sstable files from the Apache Cassandra cluster to a local folder on the intermediate node." - does it mean one folder at intermediate node for whole cluster data? I wasn't sure...

Each folder in the intermediate node will be for each KS -> table. To that table folder you copy the sstable files from that table's snapshot that you took.
When you will use the sstableloader it requires the folder path to look like this: 

• sstableloader -x -d [Scylla IP] .../[ks]/[table]

About q4 I found at point 7 -
"We recommend running several sstableloaders in parallel and utilizing all Scylla nodes as targets for sstable loading. Start with one keyspace and its underlying sstable files from all Apache Cassandra nodes. After completion, continue to the next keyspace and so on."
Does it mean configuration, where, from intermediate node, we run one Scylla sstableloader task per each Cassandra keyspace, AND every task will have one Scylla destination host per each task?

Yes. You install on each intermediate node scylla-tools-core pkg and run the sstableloader/s from each intermediate node. Each sstableloader task will be to 1 Scylla node IP destination, it doesn't matter which one.

Sorry, I wasn't sure, am I understand it correctly or not. I prefer ask before, than after

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[Tomer Sandler]

Inline.

On Wed, Jan 24, 2018 at 5:04 PM, Ilya Shibaev <ishi...@gmail.com> wrote:

and about question 5 -
I think then, it's necessary to create another topic, because I tried 'v' flag, but there are no messages... There are no bad result, no data in scylla...

Perhaps you were doing something incorrect. like the path naming convention the sstableloader expects?

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