perf: Stream BigQuery results to Cloud Storage to prevent OOM errors

Refactored the BigQuery to Google Cloud Storage export process to use streams instead of loading the entire result set into a massive memory array. This resolves potential Out-Of-Memory (OOM) errors in Cloud Run and significantly improves overall memory efficiency for large exports.

- Updated `infra/dataform-service/src/index.js` to utilize `bigquery.queryResultsStream()`.
- Refactored `StorageUpload.exportToJson` in `infra/dataform-service/src/storage.js` to accept a stream.
- Implemented a custom `Transform` stream to efficiently format object chunks into a proper JSON array structure while buffering in batches of 1000 for high performance.
- Removed unused memory-bound `Readable` initialization from `StorageUpload` constructor.

Author: max-ostapenko

infra/dataform-service/src/index.js

@@ -95,9 +95,9 @@ async function handleExport (req, res) {
       console.info('Cloud Storage export')
       console.log(query, config)
 
-      const data = await bigquery.queryResults(query)
+      const stream = await bigquery.queryResultsStream(query)
       const storage = new StorageUpload(config.bucket)
-      await storage.exportToJson(data, config.name)
+      await storage.exportToJson(stream, config.name)
     } else if (destination === 'firestore') {
       console.info('Firestore export')
       const jobName = `projects/${projectId}/locations/${location}/jobs/${jobId}`

infra/dataform-service/src/storage.js

@@ -1,30 +1,75 @@
 import { Storage } from '@google-cloud/storage'
-import { Readable } from 'stream'
+import { Transform } from 'stream'
 import zlib from 'zlib'
 
 const storage = new Storage()
 
 export class StorageUpload {
   constructor (bucket) {
     this.bucket = bucket
-    this.stream = new Readable({
-      objectMode: true,
-      read () {}
-    })
   }
 
-  async exportToJson (data, fileName) {
+  async exportToJson (stream, fileName) {
     const bucket = storage.bucket(this.bucket)
     const file = bucket.file(fileName)
 
-    const jsonData = JSON.stringify(data)
-    this.stream.push(jsonData)
-    this.stream.push(null)
+    let first = true
+    let batch = []
+    const BATCH_SIZE = 1000
+
+    const jsonTransform = new Transform({
+      writableObjectMode: true,
+      transform (chunk, encoding, callback) {
+        batch.push(chunk)
+        if (batch.length >= BATCH_SIZE) {
+          let str = ''
+          if (first) {
+            str = '[\n  ' + JSON.stringify(batch[0])
+            for (let i = 1; i < batch.length; i++) {
+              str += ',\n  ' + JSON.stringify(batch[i])
+            }
+            first = false
+          } else {
+            for (let i = 0; i < batch.length; i++) {
+              str += ',\n  ' + JSON.stringify(batch[i])
+            }
+          }
+          batch = []
+          callback(null, str)
+        } else {
+          callback()
+        }
+      },
+      flush (callback) {
+        let str = ''
+        if (batch.length > 0) {
+          if (first) {
+            str = '[\n  ' + JSON.stringify(batch[0])
+            for (let i = 1; i < batch.length; i++) {
+              str += ',\n  ' + JSON.stringify(batch[i])
+            }
+            first = false
+          } else {
+            for (let i = 0; i < batch.length; i++) {
+              str += ',\n  ' + JSON.stringify(batch[i])
+            }
+          }
+        }
+
+        if (first) {
+          str += '[]'
+        } else {
+          str += '\n]'
+        }
+        callback(null, str)
+      }
+    })
 
     const gzip = zlib.createGzip()
 
     await new Promise((resolve, reject) => {
-      this.stream
+      stream
+        .pipe(jsonTransform)
         .pipe(gzip)
         .pipe(file.createWriteStream({
           metadata: {