maxwellguo created CASSANDRA-15844:
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Summary: Create table Asynchronously or contact the same node from
many client threads at same time may causing data lose
Key: CASSANDRA-15844
URL: https://issues.apache.org/jira/browse/CASSANDRA-15844
Project: Cassandra
Issue Type: Bug
Components: Cluster/Schema
Reporter: maxwellguo
Assignee: maxwellguo
Attachments: createkeyspace.jpg, keyspace inner.jpg, schemaversion.jpg
When creating a table from on one coordinator node from some client threads at
the same time, Or creating a table using session.executeAsync() method, may
cause the schema'information incorrect. Seriously will causing data lose.
For my test. I use executeAsync() to create table one by one using the same
table name (Though I do konw create table should be synchronously, but some of
our customers may create table using executAsync() ). My expectations is that
the last cql
{code:java}
CREATE TABLE ks.tb (name text PRIMARY KEY , age int, adds text, height text)
{code}
should take effect .
!createkeyspace.jpg!
But after runing the code, I foud that the result is not what I am expected.
the schema struct is is :
{code:java}
CREATE TABLE ks.tb (name text PRIMARY KEY , age int, adds text, sex int, height
int)
{code}
!keyspace inner.jpg!
And the schema version in the memory and on the disk is not the same.
!schemaversion.jpg!
When add a new columnfamily (creat a new table), the request of creating same
table with different schema definition arrived at the same time from different
clients or using
executeAsync method.
{code:java}
private static void announceNewColumnFamily(CFMetaData cfm, boolean
announceLocally, boolean throwOnDuplicate, long timestamp) throws
ConfigurationException
{
cfm.validate();
KeyspaceMetadata ksm = Schema.instance.getKSMetaData(cfm.ksName);
if (ksm == null)
throw new ConfigurationException(String.format("Cannot add table
'%s' to non existing keyspace '%s'.", cfm.cfName, cfm.ksName));
// If we have a table or a view which has the same name, we can't add a
new one
else if (throwOnDuplicate && ksm.getTableOrViewNullable(cfm.cfName) !=
null)
throw new AlreadyExistsException(cfm.ksName, cfm.cfName);
logger.info("Create new table: {}", cfm);
announce(SchemaKeyspace.makeCreateTableMutation(ksm, cfm, timestamp),
announceLocally);
}
{code}
The code of checking table existance may failed. And same table's request may
all going to do announce() method;
{code:java}
public static synchronized void mergeSchema(Collection<Mutation> mutations,
boolean forDynamoTTL)
{
// only compare the keyspaces affected by this set of schema mutations
Set<String> affectedKeyspaces =
mutations.stream()
.map(m -> UTF8Type.instance.compose(m.key().getKey()))
.collect(Collectors.toSet());
// fetch the current state of schema for the affected keyspaces only
Keyspaces before = Schema.instance.getKeyspaces(affectedKeyspaces);
// apply the schema mutations and flush
mutations.forEach(Mutation::apply);
if (FLUSH_SCHEMA_TABLES)
flush();
// fetch the new state of schema from schema tables (not applied to
Schema.instance yet)
Keyspaces after = fetchKeyspacesOnly(affectedKeyspaces);
mergeSchema(before, after);
scheduleDynamoTTLClean(forDynamoTTL, mutations);
}
{code}
For we may write the new table definition into disk, so at last we saw
{code:java}
CREATE TABLE ks.tb (name text PRIMARY KEY , age int, adds text, sex int, height
int)
{code}
in our case.
And we also saw the different version in memory and disk.
when writing data we using the schema in memory, but when we doing node restart
the schema definition on disk will be used. Then may causing data lose.
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