From aefa8617235d84535bcd7540cb68e473fec6139b Mon Sep 17 00:00:00 2001
From: nicktrn <55853254+nicktrn@users.noreply.github.com>
Date: Tue, 30 Jun 2026 11:16:59 +0100
Subject: [PATCH 1/4] feat(webapp): add runsList clickhouse client for
 dedicated runs list reads

Runs list reads (dashboard list, runs list API, live reload, child-status
counts) went through the shared standard client (CLICKHOUSE_URL). Add a
dedicated runsList client type backed by RUNS_LIST_CLICKHOUSE_URL so this
high-traffic read path can target a read replica without moving ingest or
replication writes off CLICKHOUSE_URL. Falls back to CLICKHOUSE_URL when
unset, so it is a no-op unless configured.
---
 .server-changes/runs-list-clickhouse-url.md   |  6 ++++
 apps/webapp/app/env.server.ts                 | 14 ++++++++
 .../v3/ApiRunListPresenter.server.ts          |  2 +-
 .../route.tsx                                 |  2 +-
 ...am.env.$envParam.runs.children-statuses.ts |  2 +-
 ...s.$projectParam.env.$envParam.runs.live.ts |  2 +-
 .../clickhouse/clickhouseFactory.server.ts    | 36 ++++++++++++++++++-
 7 files changed, 59 insertions(+), 5 deletions(-)
 create mode 100644 .server-changes/runs-list-clickhouse-url.md

diff --git a/.server-changes/runs-list-clickhouse-url.md b/.server-changes/runs-list-clickhouse-url.md
new file mode 100644
index 00000000000..6048456aa4d
--- /dev/null
+++ b/.server-changes/runs-list-clickhouse-url.md
@@ -0,0 +1,6 @@
+---
+area: webapp
+type: improvement
+---
+
+Add `RUNS_LIST_CLICKHOUSE_URL` so runs list reads (dashboard, API, live reload, child-status counts) can use a dedicated ClickHouse client. Falls back to `CLICKHOUSE_URL` when unset, so it's a no-op unless configured.
diff --git a/apps/webapp/app/env.server.ts b/apps/webapp/app/env.server.ts
index d9c97711940..634f84e9cd3 100644
--- a/apps/webapp/app/env.server.ts
+++ b/apps/webapp/app/env.server.ts
@@ -1716,6 +1716,20 @@ const EnvironmentSchema = z
       .enum(["log", "error", "warn", "info", "debug"])
       .default("info"),
     REALTIME_BACKEND_NATIVE_CLICKHOUSE_COMPRESSION_REQUEST: z.string().default("1"),
+    // Dedicated ClickHouse pool for the runs list (dashboard + API). Lets us point
+    // the highest-traffic read path at a read replica without moving ingest/replication
+    // writes off CLICKHOUSE_URL. Falls back to CLICKHOUSE_URL when unset.
+    RUNS_LIST_CLICKHOUSE_URL: z
+      .string()
+      .optional()
+      .transform((v) => v ?? process.env.CLICKHOUSE_URL),
+    RUNS_LIST_CLICKHOUSE_KEEP_ALIVE_ENABLED: z.string().default("1"),
+    RUNS_LIST_CLICKHOUSE_KEEP_ALIVE_IDLE_SOCKET_TTL_MS: z.coerce.number().int().optional(),
+    RUNS_LIST_CLICKHOUSE_MAX_OPEN_CONNECTIONS: z.coerce.number().int().default(10),
+    RUNS_LIST_CLICKHOUSE_LOG_LEVEL: z
+      .enum(["log", "error", "warn", "info", "debug"])
+      .default("info"),
+    RUNS_LIST_CLICKHOUSE_COMPRESSION_REQUEST: z.string().default("1"),
     EVENTS_CLICKHOUSE_BATCH_SIZE: z.coerce.number().int().default(1000),
     EVENTS_CLICKHOUSE_FLUSH_INTERVAL_MS: z.coerce.number().int().default(1000),
     METRICS_CLICKHOUSE_BATCH_SIZE: z.coerce.number().int().default(10000),
diff --git a/apps/webapp/app/presenters/v3/ApiRunListPresenter.server.ts b/apps/webapp/app/presenters/v3/ApiRunListPresenter.server.ts
index 0e7077b3dfc..794e47bf0ea 100644
--- a/apps/webapp/app/presenters/v3/ApiRunListPresenter.server.ts
+++ b/apps/webapp/app/presenters/v3/ApiRunListPresenter.server.ts
@@ -269,7 +269,7 @@ export class ApiRunListPresenter extends BasePresenter {
         options.machines = searchParams["filter[machine]"];
       }
 
-      const clickhouse = await clickhouseFactory.getClickhouseForOrganization(organizationId, "standard");
+      const clickhouse = await clickhouseFactory.getClickhouseForOrganization(organizationId, "runsList");
       const presenter = new NextRunListPresenter(this._replica, clickhouse);
 
       logger.debug("Calling RunListPresenter", { options });
diff --git a/apps/webapp/app/routes/_app.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs._index/route.tsx b/apps/webapp/app/routes/_app.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs._index/route.tsx
index 25cccaede8e..28ffc6913c0 100644
--- a/apps/webapp/app/routes/_app.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs._index/route.tsx
+++ b/apps/webapp/app/routes/_app.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs._index/route.tsx
@@ -95,7 +95,7 @@ export const loader = async ({ request, params }: LoaderFunctionArgs) => {
 
   const clickhouse = await clickhouseFactory.getClickhouseForOrganization(
     project.organizationId,
-    "standard"
+    "runsList"
   );
   const presenter = new NextRunListPresenter($replica, clickhouse);
   const list = presenter.call(project.organizationId, environment.id, {
diff --git a/apps/webapp/app/routes/resources.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.children-statuses.ts b/apps/webapp/app/routes/resources.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.children-statuses.ts
index 896dd25dd79..920301f1662 100644
--- a/apps/webapp/app/routes/resources.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.children-statuses.ts
+++ b/apps/webapp/app/routes/resources.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.children-statuses.ts
@@ -67,7 +67,7 @@ export async function loader({ request, params }: LoaderFunctionArgs) {
 
   const clickhouse = await clickhouseFactory.getClickhouseForOrganization(
     project.organizationId,
-    "standard"
+    "runsList"
   );
   const runsRepository = new RunsRepository({ clickhouse, prisma: $replica });
 
diff --git a/apps/webapp/app/routes/resources.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.live.ts b/apps/webapp/app/routes/resources.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.live.ts
index 616aa728872..0da28c4538b 100644
--- a/apps/webapp/app/routes/resources.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.live.ts
+++ b/apps/webapp/app/routes/resources.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.live.ts
@@ -34,7 +34,7 @@ export async function loader({ request, params }: LoaderFunctionArgs) {
 
   const clickhouse = await clickhouseFactory.getClickhouseForOrganization(
     project.organizationId,
-    "standard"
+    "runsList"
   );
   const runsRepository = new RunsRepository({ clickhouse, prisma: $replica });
 
diff --git a/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts b/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts
index 7c20dd3a2a5..cfea1e2e4f2 100644
--- a/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts
+++ b/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts
@@ -242,6 +242,36 @@ function initializeRealtimeClickhouseClient(): ClickHouse {
   });
 }
 
+/** Runs list reads — dashboard + API (`RUNS_LIST_CLICKHOUSE_URL`);
+ *  falls back to the default client if unset. */
+const defaultRunsListClickhouseClient = singleton(
+  "runsListClickhouseClient",
+  initializeRunsListClickhouseClient
+);
+
+function initializeRunsListClickhouseClient(): ClickHouse {
+  if (!env.RUNS_LIST_CLICKHOUSE_URL) {
+    return defaultClickhouseClient;
+  }
+
+  const url = new URL(env.RUNS_LIST_CLICKHOUSE_URL);
+  url.searchParams.delete("secure");
+
+  return new ClickHouse({
+    url: url.toString(),
+    name: "runs-list-clickhouse",
+    keepAlive: {
+      enabled: env.RUNS_LIST_CLICKHOUSE_KEEP_ALIVE_ENABLED === "1",
+      idleSocketTtl: env.RUNS_LIST_CLICKHOUSE_KEEP_ALIVE_IDLE_SOCKET_TTL_MS,
+    },
+    logLevel: env.RUNS_LIST_CLICKHOUSE_LOG_LEVEL,
+    compression: {
+      request: env.RUNS_LIST_CLICKHOUSE_COMPRESSION_REQUEST === "1",
+    },
+    maxOpenConnections: env.RUNS_LIST_CLICKHOUSE_MAX_OPEN_CONNECTIONS,
+  });
+}
+
 /** Task events (`EVENTS_CLICKHOUSE_URL`); not exported — accessed via factory. */
 const defaultEventsClickhouseClient = singleton(
   "eventsClickhouseClient",
@@ -289,7 +319,8 @@ export type ClientType =
   | "query"
   | "admin"
   | "engine"
-  | "realtime";
+  | "realtime"
+  | "runsList";
 
 function buildOrgClickhouseClient(url: string, clientType: ClientType): ClickHouse {
   const parsed = new URL(url);
@@ -379,6 +410,7 @@ function buildOrgClickhouseClient(url: string, clientType: ClientType): ClickHou
     case "standard":
     case "query":
     case "admin":
+    case "runsList":
       return new ClickHouse({
         url: parsed.toString(),
         name,
@@ -446,6 +478,8 @@ export class ClickhouseFactory {
           return defaultRunEngineClickhouseClient;
         case "realtime":
           return defaultRealtimeClickhouseClient;
+        case "runsList":
+          return defaultRunsListClickhouseClient;
       }
     }
 

From 99ef921dc19fe1873ef92503613ad84da45a625d Mon Sep 17 00:00:00 2001
From: nicktrn <55853254+nicktrn@users.noreply.github.com>
Date: Tue, 30 Jun 2026 11:34:22 +0100
Subject: [PATCH 2/4] feat(webapp): add CLICKHOUSE_READER_URL to route reads to
 a replica

Read-only clients (logs, query, admin, runsList, engine, realtime) now fall
back X_CLICKHOUSE_URL ?? CLICKHOUSE_READER_URL ?? CLICKHOUSE_URL, and the
events client uses the reader/writer split so trace/span/log reads hit the
replica while event + log inserts stay on the writer. Set CLICKHOUSE_READER_URL
once to move all reads off the primary. Writes (events, replication,
sessions_replication, standard) always stay on CLICKHOUSE_URL. No-op when
CLICKHOUSE_READER_URL is unset.
---
 .server-changes/clickhouse-reader-url.md      |  6 ++++
 .server-changes/runs-list-clickhouse-url.md   |  2 +-
 apps/webapp/app/env.server.ts                 | 17 ++++++----
 .../clickhouse/clickhouseFactory.server.ts    | 31 ++++++++++++++++---
 4 files changed, 44 insertions(+), 12 deletions(-)
 create mode 100644 .server-changes/clickhouse-reader-url.md

diff --git a/.server-changes/clickhouse-reader-url.md b/.server-changes/clickhouse-reader-url.md
new file mode 100644
index 00000000000..8e23a51f3ee
--- /dev/null
+++ b/.server-changes/clickhouse-reader-url.md
@@ -0,0 +1,6 @@
+---
+area: webapp
+type: improvement
+---
+
+Add `CLICKHOUSE_READER_URL` to route ClickHouse reads to a read replica while writes stay on `CLICKHOUSE_URL`. Optional; defaults to `CLICKHOUSE_URL`.
diff --git a/.server-changes/runs-list-clickhouse-url.md b/.server-changes/runs-list-clickhouse-url.md
index 6048456aa4d..b0640fb34bf 100644
--- a/.server-changes/runs-list-clickhouse-url.md
+++ b/.server-changes/runs-list-clickhouse-url.md
@@ -3,4 +3,4 @@ area: webapp
 type: improvement
 ---
 
-Add `RUNS_LIST_CLICKHOUSE_URL` so runs list reads (dashboard, API, live reload, child-status counts) can use a dedicated ClickHouse client. Falls back to `CLICKHOUSE_URL` when unset, so it's a no-op unless configured.
+Add `RUNS_LIST_CLICKHOUSE_URL` to send runs list queries to a separate ClickHouse instance. Defaults to `CLICKHOUSE_URL`.
diff --git a/apps/webapp/app/env.server.ts b/apps/webapp/app/env.server.ts
index 634f84e9cd3..6137eb94a1f 100644
--- a/apps/webapp/app/env.server.ts
+++ b/apps/webapp/app/env.server.ts
@@ -1627,6 +1627,11 @@ const EnvironmentSchema = z
 
     // Clickhouse
     CLICKHOUSE_URL: z.string(),
+    // Optional read replica endpoint. Read-only clients (logs, query, admin, runsList,
+    // engine, realtime) and the events client's READ path default to this when their own
+    // URL is unset; writes always stay on CLICKHOUSE_URL. Set once to move all reads to a
+    // replica. Must share storage with the CLICKHOUSE_URL warehouse.
+    CLICKHOUSE_READER_URL: z.string().optional(),
     CLICKHOUSE_KEEP_ALIVE_ENABLED: z.string().default("1"),
     CLICKHOUSE_KEEP_ALIVE_IDLE_SOCKET_TTL_MS: z.coerce.number().int().optional(),
     CLICKHOUSE_MAX_OPEN_CONNECTIONS: z.coerce.number().int().default(10),
@@ -1653,13 +1658,13 @@ const EnvironmentSchema = z
     LOGS_CLICKHOUSE_URL: z
       .string()
       .optional()
-      .transform((v) => v ?? process.env.CLICKHOUSE_URL),
+      .transform((v) => v ?? process.env.CLICKHOUSE_READER_URL ?? process.env.CLICKHOUSE_URL),
 
     // Query page ClickHouse limits (for TSQL queries)
     QUERY_CLICKHOUSE_URL: z
       .string()
       .optional()
-      .transform((v) => v ?? process.env.CLICKHOUSE_URL),
+      .transform((v) => v ?? process.env.CLICKHOUSE_READER_URL ?? process.env.CLICKHOUSE_URL),
     QUERY_CLICKHOUSE_MAX_EXECUTION_TIME: z.coerce.number().int().default(10),
     QUERY_CLICKHOUSE_MAX_MEMORY_USAGE: z.coerce.number().int().default(1_073_741_824), // 1GB in bytes
     QUERY_CLICKHOUSE_MAX_AST_ELEMENTS: z.coerce.number().int().default(4_000_000),
@@ -1678,7 +1683,7 @@ const EnvironmentSchema = z
     ADMIN_CLICKHOUSE_URL: z
       .string()
       .optional()
-      .transform((v) => v ?? process.env.CLICKHOUSE_URL),
+      .transform((v) => v ?? process.env.CLICKHOUSE_READER_URL ?? process.env.CLICKHOUSE_URL),
 
     EVENTS_CLICKHOUSE_URL: z
       .string()
@@ -1696,7 +1701,7 @@ const EnvironmentSchema = z
     RUN_ENGINE_CLICKHOUSE_URL: z
       .string()
       .optional()
-      .transform((v) => v ?? process.env.CLICKHOUSE_URL),
+      .transform((v) => v ?? process.env.CLICKHOUSE_READER_URL ?? process.env.CLICKHOUSE_URL),
     RUN_ENGINE_CLICKHOUSE_KEEP_ALIVE_ENABLED: z.string().default("1"),
     RUN_ENGINE_CLICKHOUSE_KEEP_ALIVE_IDLE_SOCKET_TTL_MS: z.coerce.number().int().optional(),
     RUN_ENGINE_CLICKHOUSE_MAX_OPEN_CONNECTIONS: z.coerce.number().int().default(5),
@@ -1708,7 +1713,7 @@ const EnvironmentSchema = z
     REALTIME_BACKEND_NATIVE_CLICKHOUSE_URL: z
       .string()
       .optional()
-      .transform((v) => v ?? process.env.CLICKHOUSE_URL),
+      .transform((v) => v ?? process.env.CLICKHOUSE_READER_URL ?? process.env.CLICKHOUSE_URL),
     REALTIME_BACKEND_NATIVE_CLICKHOUSE_KEEP_ALIVE_ENABLED: z.string().default("1"),
     REALTIME_BACKEND_NATIVE_CLICKHOUSE_KEEP_ALIVE_IDLE_SOCKET_TTL_MS: z.coerce.number().int().optional(),
     REALTIME_BACKEND_NATIVE_CLICKHOUSE_MAX_OPEN_CONNECTIONS: z.coerce.number().int().default(10),
@@ -1722,7 +1727,7 @@ const EnvironmentSchema = z
     RUNS_LIST_CLICKHOUSE_URL: z
       .string()
       .optional()
-      .transform((v) => v ?? process.env.CLICKHOUSE_URL),
+      .transform((v) => v ?? process.env.CLICKHOUSE_READER_URL ?? process.env.CLICKHOUSE_URL),
     RUNS_LIST_CLICKHOUSE_KEEP_ALIVE_ENABLED: z.string().default("1"),
     RUNS_LIST_CLICKHOUSE_KEEP_ALIVE_IDLE_SOCKET_TTL_MS: z.coerce.number().int().optional(),
     RUNS_LIST_CLICKHOUSE_MAX_OPEN_CONNECTIONS: z.coerce.number().int().default(10),
diff --git a/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts b/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts
index cfea1e2e4f2..ffcdab86e28 100644
--- a/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts
+++ b/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts
@@ -283,12 +283,10 @@ function initializeEventsClickhouseClient(): ClickHouse {
     throw new Error("EVENTS_CLICKHOUSE_URL is not set");
   }
 
-  const url = new URL(env.EVENTS_CLICKHOUSE_URL);
-  url.searchParams.delete("secure");
+  const writerUrl = new URL(env.EVENTS_CLICKHOUSE_URL);
+  writerUrl.searchParams.delete("secure");
 
-  return new ClickHouse({
-    url: url.toString(),
-    name: "task-events",
+  const commonConfig = {
     keepAlive: {
       enabled: env.EVENTS_CLICKHOUSE_KEEP_ALIVE_ENABLED === "1",
       idleSocketTtl: env.EVENTS_CLICKHOUSE_KEEP_ALIVE_IDLE_SOCKET_TTL_MS,
@@ -298,6 +296,29 @@ function initializeEventsClickhouseClient(): ClickHouse {
       request: env.EVENTS_CLICKHOUSE_COMPRESSION_REQUEST === "1",
     },
     maxOpenConnections: env.EVENTS_CLICKHOUSE_MAX_OPEN_CONNECTIONS,
+  };
+
+  // This client both inserts events and reads traces/spans/logs. When a reader replica
+  // is configured, split it so queries hit the replica while inserts stay on the writer.
+  if (env.CLICKHOUSE_READER_URL) {
+    const readerUrl = new URL(env.CLICKHOUSE_READER_URL);
+    readerUrl.searchParams.delete("secure");
+
+    if (readerUrl.toString() !== writerUrl.toString()) {
+      return new ClickHouse({
+        ...commonConfig,
+        writerName: "task-events-writer",
+        writerUrl: writerUrl.toString(),
+        readerName: "task-events-reader",
+        readerUrl: readerUrl.toString(),
+      });
+    }
+  }
+
+  return new ClickHouse({
+    ...commonConfig,
+    name: "task-events",
+    url: writerUrl.toString(),
   });
 }
 

From ceb1bcb9dfbf071883906716ba7edc03cd2c096d Mon Sep 17 00:00:00 2001
From: nicktrn <55853254+nicktrn@users.noreply.github.com>
Date: Tue, 30 Jun 2026 12:00:46 +0100
Subject: [PATCH 3/4] feat(webapp): route run detail nav list through runsList
 client

The run detail page loads a small prev/next navigation list via
NextRunListPresenter; point it at the runsList client too so all runs list
reads use the same dedicated client.
---
 .../route.tsx                                                   | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/apps/webapp/app/routes/_app.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.$runParam/route.tsx b/apps/webapp/app/routes/_app.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.$runParam/route.tsx
index fbe4b9046c6..b2c495474f8 100644
--- a/apps/webapp/app/routes/_app.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.$runParam/route.tsx
+++ b/apps/webapp/app/routes/_app.orgs.$organizationSlug.projects.$projectParam.env.$envParam.runs.$runParam/route.tsx
@@ -190,7 +190,7 @@ async function getRunsListFromTableState({
       return null;
     }
 
-    const clickhouse = await clickhouseFactory.getClickhouseForOrganization(project.organizationId, "standard");
+    const clickhouse = await clickhouseFactory.getClickhouseForOrganization(project.organizationId, "runsList");
     const runsListPresenter = new NextRunListPresenter($replica, clickhouse);
     const currentPageResult = await runsListPresenter.call(project.organizationId, environment.id, {
       userId,

From 00bee0f4a8254e5514681b79bf4c57d80c7262ff Mon Sep 17 00:00:00 2001
From: nicktrn <55853254+nicktrn@users.noreply.github.com>
Date: Tue, 30 Jun 2026 13:35:18 +0100
Subject: [PATCH 4/4] feat(webapp): add EVENTS_READER_CLICKHOUSE_URL for events
 read replica

The events client both inserts events and reads traces/spans/logs through one
instance. Give it a dedicated reader URL so reads can move to a replica while
inserts stay on EVENTS_CLICKHOUSE_URL. Unlike the read-only clients, it does
not fall back to CLICKHOUSE_READER_URL: a write-capable client only moves reads
on an explicit opt-in.
---
 .server-changes/events-reader-clickhouse-url.md            | 6 ++++++
 apps/webapp/app/env.server.ts                              | 2 ++
 .../app/services/clickhouse/clickhouseFactory.server.ts    | 7 +++----
 3 files changed, 11 insertions(+), 4 deletions(-)
 create mode 100644 .server-changes/events-reader-clickhouse-url.md

diff --git a/.server-changes/events-reader-clickhouse-url.md b/.server-changes/events-reader-clickhouse-url.md
new file mode 100644
index 00000000000..3290ae629da
--- /dev/null
+++ b/.server-changes/events-reader-clickhouse-url.md
@@ -0,0 +1,6 @@
+---
+area: webapp
+type: improvement
+---
+
+Add `EVENTS_READER_CLICKHOUSE_URL` to send trace/span/log reads to a read replica while event inserts stay on `EVENTS_CLICKHOUSE_URL`. Optional; unset keeps reads and writes on the same instance.
diff --git a/apps/webapp/app/env.server.ts b/apps/webapp/app/env.server.ts
index 6137eb94a1f..df85b4c2116 100644
--- a/apps/webapp/app/env.server.ts
+++ b/apps/webapp/app/env.server.ts
@@ -1689,6 +1689,8 @@ const EnvironmentSchema = z
       .string()
       .optional()
       .transform((v) => v ?? process.env.CLICKHOUSE_URL),
+    // Events read replica (traces/spans/logs). No CLICKHOUSE_READER_URL fallback by design: this write-capable client opts in explicitly.
+    EVENTS_READER_CLICKHOUSE_URL: z.string().optional(),
     EVENTS_CLICKHOUSE_KEEP_ALIVE_ENABLED: z.string().default("1"),
     EVENTS_CLICKHOUSE_KEEP_ALIVE_IDLE_SOCKET_TTL_MS: z.coerce.number().int().optional(),
     EVENTS_CLICKHOUSE_MAX_OPEN_CONNECTIONS: z.coerce.number().int().default(10),
diff --git a/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts b/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts
index ffcdab86e28..69828708f8b 100644
--- a/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts
+++ b/apps/webapp/app/services/clickhouse/clickhouseFactory.server.ts
@@ -298,10 +298,9 @@ function initializeEventsClickhouseClient(): ClickHouse {
     maxOpenConnections: env.EVENTS_CLICKHOUSE_MAX_OPEN_CONNECTIONS,
   };
 
-  // This client both inserts events and reads traces/spans/logs. When a reader replica
-  // is configured, split it so queries hit the replica while inserts stay on the writer.
-  if (env.CLICKHOUSE_READER_URL) {
-    const readerUrl = new URL(env.CLICKHOUSE_READER_URL);
+  // Mixed read+write client: split reads to its own EVENTS_READER_CLICKHOUSE_URL (not the global reader) so inserts can never hit the replica.
+  if (env.EVENTS_READER_CLICKHOUSE_URL) {
+    const readerUrl = new URL(env.EVENTS_READER_CLICKHOUSE_URL);
     readerUrl.searchParams.delete("secure");
 
     if (readerUrl.toString() !== writerUrl.toString()) {