fix(clickhouse): tune memory settings to prevent OOM on insert

ClickHouse 24.12 auto-sizes caches from the cgroup limit, leaving
insufficient headroom for MV processing and background merges.
Adds a custom config that shrinks mark/index/expression caches and
caps per-query memory at 2 GiB. Bumps container limit 4Gi → 6Gi.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

deploy/clickhouse.yaml

@@ -40,12 +40,16 @@ spec:
               mountPath: /var/lib/clickhouse
             - name: initdb
               mountPath: /docker-entrypoint-initdb.d
+            - name: config
+              mountPath: /etc/clickhouse-server/config.d/memory-tuning.xml
+              subPath: memory-tuning.xml
+              readOnly: true
           resources:
             requests:
               memory: "2Gi"
               cpu: "500m"
             limits:
-              memory: "4Gi"
+              memory: "6Gi"
               cpu: "2000m"
           livenessProbe:
             httpGet:
@@ -67,6 +71,9 @@ spec:
         - name: initdb
           configMap:
             name: clickhouse-initdb
+        - name: config
+          configMap:
+            name: clickhouse-config
   volumeClaimTemplates:
     - metadata:
         name: data
@@ -95,6 +102,36 @@ spec:
 ---
 apiVersion: v1
 kind: ConfigMap
+metadata:
+  name: clickhouse-config
+  namespace: cameleer
+data:
+  memory-tuning.xml: |
+    <clickhouse>
+        <!-- Fit comfortably in a 6Gi container (cgroup limit).                  -->
+        <!-- Without this file ClickHouse auto-sizes caches and buffers from the -->
+        <!-- cgroup limit, leaving almost no room for query execution.           -->
+
+        <!-- Cap any single query/insert (including MV processing) at 2 GiB -->
+        <profiles>
+            <default>
+                <max_memory_usage>2147483648</max_memory_usage>
+            </default>
+        </profiles>
+
+        <!-- Shrink internal caches — defaults are sized for beefy servers -->
+        <mark_cache_size>134217728</mark_cache_size>
+        <index_mark_cache_size>67108864</index_mark_cache_size>
+        <uncompressed_cache_size>0</uncompressed_cache_size>
+        <compiled_expression_cache_size>67108864</compiled_expression_cache_size>
+
+        <merge_tree>
+            <max_bytes_to_merge_at_max_space_in_pool>536870912</max_bytes_to_merge_at_max_space_in_pool>
+        </merge_tree>
+    </clickhouse>
+---
+apiVersion: v1
+kind: ConfigMap
 metadata:
   name: clickhouse-initdb
   namespace: cameleer