[HUD] Add merge retry rate calculation metric (#6957)

Adds the metric that calculates the average number of merge attempts it
takes to merge the PR in.

Only counts attempts up to when the PR was closed/merged the first time
(for simplicity).

Excludes pytorchupdatebot PRs.


### Testing 
* locally
* query perf:
```
+------+----------+-----------+
| Test | Avg Time |  Avg Mem  |
+------+----------+-----------+
|  0   |   2201   | 280219309 |
|  1   |   1290   | 275053899 |
|  2   |   1215   | 283963827 |
+------+----------+-----------+
```

Author: izaitsevfb

torchci/clickhouse_queries/merge_retry_rate/params.json

@@ -0,0 +1,20 @@
+{
+  "params": {
+    "startTime": "DateTime64(3)",
+    "stopTime": "DateTime64(3)"
+  },
+  "tests": [
+    {
+      "startTime": "2024-12-20T00:00:00.000",
+      "stopTime": "2024-12-27T00:00:00.000"
+    },
+    {
+      "startTime": "2024-12-01T00:00:00.000",
+      "stopTime": "2024-12-31T23:59:59.999"
+    },
+    {
+      "startTime": "2024-11-01T00:00:00.000",
+      "stopTime": "2024-11-30T23:59:59.999"
+    }
+  ]
+}

torchci/clickhouse_queries/merge_retry_rate/query.sql

@@ -0,0 +1,50 @@
+-- Query to calculate average merge retry rate for recent period
+-- Merge retry rate = average number of merge attempts before first successful merge
+-- Only counts attempts up to when the PR was closed/merged (proxy for dev friction)
+-- Filters by PR creation date
+-- Excludes pytorchupdatebot PRs to avoid skewing metrics with stuck bot updates
+WITH
+merged_prs AS (
+    SELECT
+        number AS pr_number,
+        parseDateTimeBestEffort(closed_at) AS merge_time,
+        parseDateTimeBestEffort(created_at) AS created_time,
+        user.login AS author
+    FROM default.pull_request
+    WHERE
+        dynamoKey LIKE 'pytorch/pytorch%'
+        AND state = 'closed'
+        AND arrayExists(x -> x.'name' = 'Merged', labels)
+        AND closed_at != ''
+        -- Filter by PR creation date
+        AND parseDateTimeBestEffort(created_at) >= {startTime: DateTime64(3)}
+        AND parseDateTimeBestEffort(created_at) <= {stopTime: DateTime64(3)}
+        -- Exclude pytorchupdatebot PRs (often stuck with many attempts)
+        AND user.login != 'pytorchupdatebot'
+),
+
+all_merge_attempts AS (
+    SELECT
+        toUInt32(extractGroups(issue_url, 'issues/([0-9]+)')[1]) AS pr_number,
+        created_at
+    FROM default.issue_comment
+    WHERE
+        dynamoKey LIKE 'pytorch/pytorch%'
+        AND user.login = 'pytorchmergebot'
+        AND body LIKE '%Merge started%'
+),
+
+attempts_per_pr AS (
+    SELECT
+        mp.pr_number,
+        COUNT(*) AS attempt_count
+    FROM merged_prs mp
+    CROSS JOIN all_merge_attempts ama
+    WHERE
+        ama.pr_number = mp.pr_number
+        AND ama.created_at <= mp.merge_time
+    GROUP BY mp.pr_number
+)
+
+SELECT ROUND(AVG(attempt_count), 2) AS avg_retry_rate
+FROM attempts_per_pr

torchci/pages/metrics.tsx

@@ -752,6 +752,28 @@ export default function Page() {
           </Stack>
         </Grid2>
 
+        <Grid2
+          container
+          size={{ xs: 6, md: 3, lg: 2 }}
+          justifyContent={"stretch"}
+        >
+          <Stack
+            justifyContent={"space-between"}
+            flexGrow={1}
+            flexWrap="wrap"
+            spacing={1}
+          >
+            <ScalarPanel
+              title={"Merge retry rate (avg)"}
+              queryName={"merge_retry_rate"}
+              metricName={"avg_retry_rate"}
+              valueRenderer={(value) => value.toFixed(2) + "x"}
+              queryParams={timeParams}
+              badThreshold={(value) => value > 2.0} // 2.0 average retries
+            />
+          </Stack>
+        </Grid2>
+
         <Grid2
           container
           size={{ xs: 6, md: 3, lg: 2 }}