PLUTON-19231 | Fewer database calls in VcLTagBuilder.prepare_redirects

Previously, related domains and domain mappings for a given cluster were fetched in a loop, performing many small selects
In this change, two types of of data fetching procedures (acquiring all domain mappings, and static domain mappings for each cluster)
have been moved to VclRendererInput, and the smaller chunks needed for rendering steps are obtained locally from simple data structures.

In local testing, this resulted in roughly halving the time of the prepare_redirects rendering phase (from around 2 to around 0.9 seconds)

vaas/vaas/vcl/renderer.py

@@ -6,6 +6,7 @@
 import time
 import functools
 from typing import Dict, List
+from urllib.parse import urlsplit
 
 from django.conf import settings
 from django.db.models import Prefetch
@@ -15,6 +16,7 @@
 from vaas.router.models import Route, Redirect
 from vaas.cluster.models import VclTemplateBlock, Dc, VclVariable, LogicalCluster, DomainMapping
 from vaas.cluster.mapping import MappingProvider
+import logging
 
 VCL_TAGS = {
     '4.0': [
@@ -186,23 +188,50 @@ def __init__(self, varnish, input_data):
             'mesh_routing': varnish.cluster.service_mesh_routing
         }
 
+    def filter_cluster_domain_mappings(
+        self, cluster: LogicalCluster
+    ) -> dict[str, list[str]]:
+        """Returns a dictionary where keys are domains, and values are mapped to by the key"""
+        # we can PROBABLY assume that each domain has only one mapping
+        # in an experiment trying to add a new mapping for a source domain removed the old one
+        destination_dict = {}
+        for domain_mapping in self.input.domain_mappings:
+            domain = domain_mapping.domain
+            destination_dict[domain] = domain_mapping.mapped_domains(cluster)
+        return destination_dict
+
+    def provide_related_domains(self, cluster: LogicalCluster) -> list[str]:
+        """Returns a list of all domains related to a cluster - for static mappings,
+        the list is specified within the mapping, for dynamic - clusters are associated using
+        labels (mapping targets can contain labels, and each cluster can have multiple labels, but
+        each label belongs to exactly one cluster)"""
+        result = {m.domain for m in self.input.static_domain_mappings_by_cluster[cluster.name]}
+        for m in self.input.mapping_provider.mappings["dynamic"]:
+            if m.is_cluster_related_by_labels(cluster):
+                result.add(m.domain)
+        return sorted(list(result))
+
     @collect_processing
     def prepare_redirects(self) -> Dict[str, List[VclRedirect]]:
         redirects = {}
-        related_domains = MappingProvider(DomainMapping.objects.all()).provide_related_domains(self.varnish.cluster) # tutaj juz mamy dwa zapytania do bazy
+        related_domains = self.provide_related_domains(self.varnish.cluster)
+        destinations_dict = self.filter_cluster_domain_mappings(self.varnish.cluster)
         for redirect in self.input.redirects:
-            destination_domain, destination_mappings = redirect.fetch_all_destinations_mappings(self.varnish.cluster) # tutaj znów sięgamy do bazy po redirecty i liste mappingow
-            if str(redirect.src_domain) in related_domains:
-                for mapped_domain in redirect.src_domain.mapped_domains(self.varnish.cluster):
-                    destination = str(redirect.destination)
-                    if destination_domain == redirect.src_domain.domain:
-                        destination = destination.replace(destination_domain, mapped_domain)
-                    elif all((destination_domain, len(destination_mappings) == 1)):
-                        destination = destination.replace(destination_domain, destination_mappings[0])
-                    if entries := redirects.get(mapped_domain, []):
-                        entries.append(VclRedirect(redirect, mapped_domain, destination))
-                    else:
-                        redirects[mapped_domain] = [VclRedirect(redirect, mapped_domain, destination)]
+            if str(redirect.src_domain) not in related_domains:
+                continue
+            destination_domain = urlsplit(redirect.destination).netloc
+            destination_mappings = destinations_dict.get(destination_domain)
+            for mapped_domain in redirect.src_domain.mapped_domains(self.varnish.cluster):
+                destination = str(redirect.destination)
+                if destination_domain == redirect.src_domain.domain:
+                    destination = destination.replace(destination_domain, mapped_domain)
+                elif destination_domain and len(destination_mappings) == 1:
+                    destination = destination.replace(destination_domain, destination_mappings[0])
+
+                if entries := redirects.get(mapped_domain, []):
+                    entries.append(VclRedirect(redirect, mapped_domain, destination))
+                else:
+                    redirects[mapped_domain] = [VclRedirect(redirect, mapped_domain, destination)]
         return redirects
 
     @collect_processing
@@ -392,6 +421,18 @@ def fetch_render_data(self):
         )
         self.distributed_backends = self.distribute_backends(backends)
         self.distributed_canary_backends = self.prepare_canary_backends(canary_backend_ids, backends)
+        self.domain_mappings = DomainMapping.objects.all()
+        self.mapping_provider = MappingProvider(self.domain_mappings)
+        self.static_domain_mappings_by_cluster = self.cluster_static_domain_mappings()
+
+    def cluster_static_domain_mappings(self) -> dict[str, list[DomainMapping]]:
+        """Returns a dict cluster.name: [associated domain mappings]"""
+        # NTH: get the same output with only one database query, perhaps with prefetch_related()
+        result_dict = dict()
+        all_clusters = LogicalCluster.objects.all()
+        for cluster in all_clusters:
+            result_dict[cluster.name] = cluster.domainmapping_set.filter(type="static")
+        return result_dict
 
     @collect_processing
     def distribute_backends(self, backends):