jameshartig commented on code in PR #1793:
URL:
https://github.com/apache/cassandra-gocql-driver/pull/1793#discussion_r1936626495
##########
session.go:
##########
@@ -1430,6 +1435,22 @@ func (q *Query) releaseAfterExecution() {
q.decRefCount()
}
+// SetHostID allows to define on which host the query should be executed.
+// If hostID is not set, then the HostSelectionPolicy will be used to pick a
host.
+// It is recommended to get host id from HostInfo.HostID(), but it is not
required.
+// It is strongly recommended to use WithContext() with this option because
+// if the specified host goes down during execution, the driver will try to
send the query to this host until it succeeds
+// which may lead to an endless execution.
+func (q *Query) SetHostID(hostID string) *Query {
+ q.hostID = hostID
Review Comment:
Passing a pointer seems a bit awkward to use and is very unusual given all
of the other functions in this package. What happens if you call
`RoutingKey(nil)` or `PageState(nil)`, etc. Setting it to empty could be a way
to unset an existing HostID if one was set for some reason prior. When queries
are immutable it could be useful to get a copy of a query without a specific
HostID that previously had one set.
We should just document that sending an empty string will restore the
default behavior.
##########
query_executor.go:
##########
@@ -83,7 +84,27 @@ func (q *queryExecutor) speculate(ctx context.Context, qry
ExecutableQuery, sp S
}
func (q *queryExecutor) executeQuery(qry ExecutableQuery) (*Iter, error) {
- hostIter := q.policy.Pick(qry)
+ var hostIter NextHost
+
+ // check if the host id is specified for the query,
+ // if it is, the query should be executed at the corresponding host.
+ if hostID := qry.GetHostID(); hostID != "" {
+ pool, ok := q.pool.getPoolByHostID(hostID)
+ if !ok || !pool.host.IsUp() {
+ return &Iter{err: ErrNoConnections}, nil
+ }
+ hostIter = func() SelectedHost {
+ // forcing hostIter to always return the same host
+ // it makes any retries and speculative executions run
on the specified host
Review Comment:
Yeah I think retries makes sense. That can always be overwritten if they
don't want that.
##########
session.go:
##########
@@ -2177,6 +2203,15 @@ func (t *traceWriter) Trace(traceId []byte) {
}
}
+// GetHosts returns a list of hosts found via queries to system.local and
system.peers
+func (s *Session) GetHosts() ([]*HostInfo, error) {
Review Comment:
We can't use the pool since it's filtered by the hostSelectionPolicy. We can
use the session's `ring.allHosts()` method though.
##########
cassandra_test.go:
##########
@@ -3338,3 +3338,56 @@ func TestQuery_NamedValues(t *testing.T) {
t.Fatal(err)
}
}
+
+func TestQuery_SetHost(t *testing.T) {
Review Comment:
`TestQuery_SetHostID`
##########
query_executor.go:
##########
@@ -41,6 +41,7 @@ type ExecutableQuery interface {
Keyspace() string
Table() string
IsIdempotent() bool
+ GetHostID() string
Review Comment:
Another option here rather than changing the `ExecutableQuery` is to do:
```go
type hostIDQuery interface {
GetHostID() string
}
```
then later in `executeQuery` you'd do:
```go
var hostID string
if hostIDQry, ok := qry.(hostIDQuery); ok {
hostID = hostIDQry.GetHostID()
}
```
Then we wouldn't need to break this interface and worry about modifying
batch.
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