Raj Ummadisetty created CASSGO-104:
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Summary: TokenAwareHostPolicy does not populate replica maps for
non-default keyspaces
Key: CASSGO-104
URL: https://issues.apache.org/jira/browse/CASSGO-104
Project: Apache Cassandra Go driver
Issue Type: Bug
Reporter: Raj Ummadisetty
h3. Problem:
When a session is created with keyspace (e.g., {color:#0747a6}ks1{color}) but
queries are executed against a different keyspace (e.g., {color:#00875a}SELECT
* FROM ks2.table{color}), the TokenAwareHostPolicy fails to perform token-aware
routing for the non-default keyspace. This occurs because the replica map
(meta.replicas) is only populated for the session's default keyspace.
This is a follow-up to issue ([GitHub
#1621|https://github.com/apache/cassandra-gocql-driver/issues/1621]). While [PR
#1714|https://github.com/apache/cassandra-gocql-driver/pull/1714] fixed the
keyspace extraction from prepared statements, it did not address the underlying
issue of populating replica information for non-default keyspaces.
h3. Impact:
* Ineffective replica shuffling: Even when ShuffleReplicas() is enabled, all
queries to non-default keyspaces go to the primary replica
* Creates uneven load distribution across the cluster
h3. Steps to Reproduce:
{code:java}
// Create session with keyspace ks1
cluster := gocql.NewCluster("127.0.0.1")
cluster.Keyspace = "ks1"
cluster.PoolConfig.HostSelectionPolicy =
gocql.TokenAwareHostPolicy(gocql.RoundRobinHostPolicy(),gocql.ShuffleReplicas))
session, _ := cluster.CreateSession()
defer session.Close()
// Query keyspace ks2
stmt := "SELECT * FROM ks2.table WHERE id = ?"
// This query will always be routed to primary replica
query := session.Query(stmt, someID)
{code}
h3. Root Cause:
In policies.go, the Pick() method looks up replicas:
[ht :=
meta.replicas[keyspace].replicasFor(token)|https://github.com/apache/cassandra-gocql-driver/blob/f1e31a58f7e0c25e58e2e2a0a0c6de358e643e8b/policies.go#L615]
However, meta.replicas[keyspace] is nil for any keyspace except the session's
default keyspace
h3. Proposed Solution
Implement lazy loading of replica maps in the Pick() method:
1. When replicas are not found for a keyspace, call a new
ensureReplicasForKeyspace() method
2. This method uses double-checked locking to populate the replica map on-demand
3. Subsequent queries to the same keyspace use the cached replica information
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