Do multi-path PATCH instead of PUT in database:import

src/commands/database-import.ts

@@ -25,7 +25,7 @@ interface DatabaseImportOptions extends Options {
   concurrency?: string;
 }
 
-const MAX_CHUNK_SIZE_MB = 10;
+const MAX_CHUNK_SIZE_MB = 1;
 const MAX_PAYLOAD_SIZE_MB = 256;
 const CONCURRENCY_LIMIT = 5;
 
@@ -47,7 +47,7 @@ export const command = new Command("database:import <path> [infile]")
     "--filter <dataPath>",
     "import only data at this path in the JSON file (if omitted, import entire file)"
   )
-  .option("--chunk-size <mb>", "max chunk size in megabytes, default to 10 MB")
+  .option("--chunk-size <mb>", "max chunk size in megabytes, default to 1 MB")
   .option("--concurrency <val>", "concurrency limit, default to 5")
   .before(requirePermissions, ["firebasedatabase.instances.update"])
   .before(requireDatabaseInstance)

src/database/import.ts

@@ -17,15 +17,105 @@ type Data = {
   pathname: string;
 };
 
+type SizedData = Data & { size: number };
+
 type ChunkedData = {
-  chunks: Data[] | null;
+  chunks: SizedData[] | null;
   size: number;
 };
 
+/**
+ * Batches chunked JSON data up to the specified byte size limit.
+ */
+class BatchChunks extends stream.Transform {
+  private batch: SizedData[] = [];
+  private size = 0;
+
+  constructor(private maxSize: number, opts?: stream.TransformOptions) {
+    super({ ...opts, objectMode: true });
+  }
+
+  _transform(chunk: SizedData, _: BufferEncoding, callback: stream.TransformCallback): void {
+    const totalChunkSize = chunk.size + chunk.pathname.length; // Overestimate
+    if (this.size + totalChunkSize > this.maxSize) {
+      this.push(this.transformBatchToPatchData(this.batch));
+      this.batch = [];
+      this.size = 0;
+    }
+    this.batch.push(chunk);
+    this.size += totalChunkSize;
+    callback(null);
+  }
+
+  private transformBatchToPatchData(batch: SizedData[]): SizedData {
+    return this.sanitizePatchData(this.compactData(batch));
+  }
+
+  private compactData(batch: SizedData[]): SizedData {
+    if (batch.length === 1) {
+      return batch[0];
+    }
+    const pathname = this.findLongestCommonPrefixArray(batch.map((d) => d.pathname));
+    let json = {};
+    let size = 0;
+    for (const chunk of batch) {
+      const truncatedPath = chunk.pathname.substring(pathname.length + 1); // +1 to trim leading slash
+      json = Object.assign({}, json, { [truncatedPath]: chunk.json });
+      size += chunk.size;
+    }
+    return { json, pathname, size };
+  }
+
+  // Since we cannot PATCH primitives and arrays, we explicitly convert them to objects.
+  private sanitizePatchData({ json, pathname, size }: SizedData): SizedData {
+    if (typeof json === "string" || typeof json === "number" || typeof json === "boolean") {
+      const tokens = pathname.split("/");
+      const lastToken = tokens.pop();
+      return { json: { [lastToken!]: json }, pathname: tokens.join("/"), size };
+    }
+    if (Array.isArray(json)) {
+      return { json: { ...json }, pathname, size };
+    }
+    return { json, pathname, size };
+  }
+
+  private findLongestCommonPrefixArray(paths: string[]): string {
+    const findLongestCommonPrefixPair = (p: string, q: string): string => {
+      const pTokens = p.split("/");
+      const qTokens = q.split("/");
+      let prefix = pTokens.slice(0, qTokens.length);
+      for (let i = 0; i < prefix.length; i++) {
+        if (prefix[i] !== qTokens[i]) {
+          prefix = prefix.slice(0, i);
+          break;
+        }
+      }
+      return prefix.join("/");
+    };
+
+    if (paths.length === 0) {
+      return "";
+    }
+    let prefix = paths[0];
+    for (let i = 1; i < paths.length; i++) {
+      prefix = findLongestCommonPrefixPair(prefix, paths[i]);
+    }
+    return prefix;
+  }
+
+  _flush(callback: stream.TransformCallback): void {
+    if (this.size > 0) {
+      this.push(this.transformBatchToPatchData(this.batch));
+    }
+    callback(null);
+  }
+}
+
 /**
  * Imports JSON data to a given RTDB instance.
  *
- * The data is parsed and chunked into subtrees of ~10 MB, to be subsequently written in parallel.
+ * The data is parsed and chunked into subtrees of the specified payload size, to be subsequently
+ * written in parallel.
  */
 export default class DatabaseImporter {
   private client: Client;
@@ -36,7 +126,7 @@ export default class DatabaseImporter {
     private dbUrl: URL,
     private inStream: stream.Readable,
     private dataPath: string,
-    private chunkBytes: number,
+    private payloadSize: number,
     concurrency: number
   ) {
     this.client = new Client({ urlPrefix: dbUrl.origin, auth: true });
@@ -68,26 +158,35 @@ export default class DatabaseImporter {
     }
   }
 
+  /**
+   * The top-level objects are parsed and chunked, with each chunk capped at payloadSize. Then,
+   * chunks are batched, with each batch also capped at payloadSize. Finally, the batched chunks
+   * are written in parallel.
+   *
+   * In the case where the data contains very large objects, chunking ensures that the request is
+   * not too large. On the other hand, in the case where the data contains many small objects,
+   * batching ensures that there are not too many requests.
+   */
   private readAndWriteChunks(): Promise<ClientResponse<JsonType>[]> {
-    const { dbUrl } = this;
+    const { dbUrl, payloadSize } = this;
     const chunkData = this.chunkData.bind(this);
-    const writeChunk = this.writeChunk.bind(this);
+    const doWriteBatch = this.doWriteBatch.bind(this);
     const getJoinedPath = this.joinPath.bind(this);
 
     const readChunks = new stream.Transform({ objectMode: true });
     readChunks._transform = function (chunk: { key: string; value: JsonType }, _, done) {
       const data = { json: chunk.value, pathname: getJoinedPath(dbUrl.pathname, chunk.key) };
       const chunkedData = chunkData(data);
-      const chunks = chunkedData.chunks || [data];
+      const chunks = chunkedData.chunks || [{ ...data, size: JSON.stringify(data.json).length }];
       for (const chunk of chunks) {
         this.push(chunk);
       }
       done();
     };
 
-    const writeChunks = new stream.Transform({ objectMode: true });
-    writeChunks._transform = async function (chunk: Data, _, done) {
-      const res = await writeChunk(chunk);
+    const writeBatch = new stream.Transform({ objectMode: true });
+    writeBatch._transform = async function (batch: SizedData, _, done) {
+      const res = await doWriteBatch(batch);
       this.push(res);
       done();
     };
@@ -115,19 +214,20 @@ export default class DatabaseImporter {
           )
         )
         .pipe(readChunks)
-        .pipe(writeChunks)
+        .pipe(new BatchChunks(payloadSize))
+        .pipe(writeBatch)
         .on("data", (res: ClientResponse<JsonType>) => responses.push(res))
         .on("error", reject)
         .once("end", () => resolve(responses));
     });
   }
 
-  private writeChunk(chunk: Data): Promise<ClientResponse<JsonType>> {
+  private doWriteBatch(batch: SizedData): Promise<ClientResponse<JsonType>> {
     const doRequest = (): Promise<ClientResponse<JsonType>> => {
       return this.client.request({
-        method: "PUT",
-        path: chunk.pathname + ".json",
-        body: JSON.stringify(chunk.json),
+        method: "PATCH",
+        path: `${batch.pathname}.json`,
+        body: batch.json,
         queryParams: this.dbUrl.searchParams,
       });
     };
@@ -157,7 +257,7 @@ export default class DatabaseImporter {
       // Children node
       let size = 2; // {}
 
-      const chunks = [];
+      const chunks: SizedData[] = [];
       let hasChunkedChild = false;
 
       for (const [key, val] of Object.entries(json)) {
@@ -170,11 +270,11 @@ export default class DatabaseImporter {
           hasChunkedChild = true;
           chunks.push(...childChunks.chunks);
         } else {
-          chunks.push(child);
+          chunks.push({ ...child, size: childChunks.size });
         }
       }
 
-      if (hasChunkedChild || size >= this.chunkBytes) {
+      if (hasChunkedChild || size >= this.payloadSize) {
         return { chunks, size };
       } else {
         return { chunks: null, size };