app/vmselect: skip caching empty responses for tenants discovery

Before, empty tenant response was cached for 5min. Making all subsequent
read queries to return empty response, even if data for the tenants was
properly ingested.

With this change empty response won't be cached.
This change is important for integration tests, where reads and writes
are performed one after another.

Signed-off-by: hagen1778 <roman@victoriametrics.com>

app/vmselect/netstorage/tenant_cache.go

@@ -47,6 +47,10 @@ func TenantsCached(qt *querytracer.Tracer, tr storage.TimeRange, deadline search
 	}
 
 	qtL.Printf("fetched %d tenants from storage", len(tenants))
+	if len(tenants) == 0 {
+		qtL.Printf("no tenants found - don't cache this fetch")
+		return nil, nil
+	}
 
 	tt := make([]storage.TenantToken, len(tenants))
 	for i, t := range tenants {

docs/victoriametrics/changelog/CHANGELOG.md

@@ -43,6 +43,7 @@ See also [LTS releases](https://docs.victoriametrics.com/victoriametrics/lts-rel
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/victoriametrics/vmagent/): prevent unintentional rerouting of samples to other sharding targets when one of the `-remoteWrite.url` targets with `-remoteWrite.disableOnDiskQueue` becomes blocked. Previously this could break the sharding guarantee by sending samples to wrong targets instead of dropping or retrying them. See [#10507](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/10507).
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/victoriametrics/vmagent/): return error on startup if `-remoteWrite.disableOnDiskQueue` is not configured uniformly across all `-remoteWrite.url` targets when `-remoteWrite.shardByURL` is enabled. Either all targets must have it enabled or all must have it disabled. See [#10507](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/10507).
 * BUGFIX: [vmsingle](https://docs.victoriametrics.com/victoriametrics/single-server-victoriametrics/) and `vmselect` in [VictoriaMetrics cluster](https://docs.victoriametrics.com/victoriametrics/cluster-victoriametrics/): hide values passed to `vmalert.proxyURL` in startup logs, `/metrics`, and `/flags`, since they can contain sensitive HTTP headers such as `Authorization` and API keys.
+* BUGFIX: `vmselect` in [VictoriaMetrics cluster](https://docs.victoriametrics.com/victoriametrics/cluster-victoriametrics/): don't cache empty responses for tenant IDs discovery during [multitenant queries](https://docs.victoriametrics.com/Cluster-VictoriaMetrics.html#multitenant-reads). This problem was visible during integration tests when multitenant queries were executed before the first ingestion happened.
 
 ## [v1.143.0](https://github.com/VictoriaMetrics/VictoriaMetrics/releases/tag/v1.143.0)