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https://issues.apache.org/jira/browse/CASSANDRA-15298?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16921676#comment-16921676
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Jeremy Hanna commented on CASSANDRA-15298:
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Ah so you're saying that beyond just dropped columns, you're looking for a more
complete way to get the snapshot of the schema because UDFs aren't stored in
the table schema data?
> Cassandra node cannot be restored using documented backup method
> ----------------------------------------------------------------
>
> Key: CASSANDRA-15298
> URL: https://issues.apache.org/jira/browse/CASSANDRA-15298
> Project: Cassandra
> Issue Type: Bug
> Reporter: Charlemange Lasse
> Priority: Normal
>
> I have a single cassandra 3.11.4 node. It contains various tables and UDFs.
> The [documentation describes a method to backup this
> node|https://docs.datastax.com/en/archived/cassandra/3.0/cassandra/operations/opsBackupTakesSnapshot.html]:
> * use "DESCRIBE SCHEMA" in cqlsh to get the schema
> * create a snapshot using nodetool
> * copy the snapshot + schema to a new (completely disconnected) node
> * load schema into new node
> * load sstables again using nodetool
> But this is a complete bogus method. It will result in errors like:
>
> {noformat}
> java.lang.RuntimeException: Unknown column deleted_column during
> deserialization {noformat}
> And all data in this column is now lost.
> Problem is that the "DESCRIBE SCHEMA" CQL doesn't add the stuff correctly for
> already deleted (but still existing columns) to the schema. It looks for
> example like:
> {noformat}
> CREATE TABLE mykeyspace.testcf (
> primary_uuid uuid,
> secondary_uuid uuid,
> name text,
> PRIMARY KEY (main_uuid, secondary_uuid)
> ) WITH CLUSTERING ORDER BY (secondary_uuid ASC)
> AND bloom_filter_fp_chance = 0.01
> AND caching = {'keys': 'ALL', 'rows_per_partition': 'NONE'}
> AND comment = ''
> AND compaction = {'class':
> 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy',
> 'max_threshold': '32', 'min_threshold': '4'}
> AND compression = {'chunk_length_in_kb': '64', 'class':
> 'org.apache.cassandra.io.compress.LZ4Compressor'}
> AND crc_check_chance = 1.0
> AND dclocal_read_repair_chance = 0.1
> AND default_time_to_live = 0
> AND gc_grace_seconds = 864000
> AND max_index_interval = 2048
> AND memtable_flush_period_in_ms = 0
> AND min_index_interval = 128
> AND read_repair_chance = 0.0
> AND speculative_retry = '99PERCENTILE';
> {noformat}
> But it must actually look like:
> {noformat}
> CREATE TABLE IF NOT EXISTS mykeyspace.testcf (
> primary_uuid uuid,
> secondary_uuid uuid,
> name text,
> deleted_column boolean,
> PRIMARY KEY (main_uuid, secondary_uuid)
> WITH ID = a1afdd4d-b61e-4f2a-b806-57c296be3948
> AND CLUSTERING ORDER BY (ap_uuid ASC)
> AND bloom_filter_fp_chance = 0.01
> AND dclocal_read_repair_chance = 0.1
> AND crc_check_chance = 1.0
> AND default_time_to_live = 0
> AND gc_grace_seconds = 864000
> AND min_index_interval = 128
> AND max_index_interval = 2048
> AND memtable_flush_period_in_ms = 0
> AND read_repair_chance = 0.0
> AND speculative_retry = '99PERCENTILE'
> AND comment = ''
> AND caching = { 'keys': 'ALL', 'rows_per_partition': 'NONE' }
> AND compaction = { 'max_threshold': '32', 'min_threshold': '4',
> 'class': 'org.apache.cassandra.db.compaction.SizeTieredCompactionStrategy' }
> AND compression = { 'chunk_length_in_kb': '64', 'class':
> 'org.apache.cassandra.io.compress.LZ4Compressor' }
> AND cdc = false
> AND extensions = { };
> ALTER TABLE mykeyspace.testcf DROP deleted_column USING TIMESTAMP
> 1563978151561000;
> {noformat}
> This was taken from the snapshot's (column family specific) schema.cql. Which
> of course is not compatible with the main schema because it will only create
> the tables when they don't exist (which they are because the main "DESCRIBE
> SCHEMA" file already creates them) and is missing all other kind of stuff
> like UDFs.
> It is currently not possible (using the builtin mechanisms from cassandra
> 3.11.4) to migrate a keyspace from one separated server to another separated
> server.
> This behavior also breaks various backup systems which try to store cassandra
> cluster information to an offline storage.
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