fix(export): stream and paginate database dumps to support large databases

Resolves OOM/timeout failures when dumping large databases by switching
the /export/dump response to a ReadableStream and paginating per-table
SELECTs with LIMIT/OFFSET instead of loading the entire result set into
memory at once.

Closes #59

Author: ThaiTrevor

src/export/dump.test.ts

@@ -128,6 +128,57 @@ describe('Database Dump Module', () => {
         )
     })
 
+    it('should paginate large tables across multiple queries', async () => {
+        const firstPage = Array.from({ length: 1000 }, (_, i) => ({
+            id: i + 1,
+            name: `User${i + 1}`,
+        }))
+        const secondPage = [{ id: 1001, name: 'User1001' }]
+
+        vi.mocked(executeOperation)
+            .mockResolvedValueOnce([{ name: 'users' }])
+            .mockResolvedValueOnce([
+                { sql: 'CREATE TABLE users (id INTEGER, name TEXT);' },
+            ])
+            .mockResolvedValueOnce(firstPage)
+            .mockResolvedValueOnce(secondPage)
+
+        const response = await dumpDatabaseRoute(mockDataSource, mockConfig)
+        const dumpText = await response.text()
+
+        expect(dumpText).toContain("INSERT INTO users VALUES (1, 'User1');")
+        expect(dumpText).toContain(
+            "INSERT INTO users VALUES (1000, 'User1000');"
+        )
+        expect(dumpText).toContain(
+            "INSERT INTO users VALUES (1001, 'User1001');"
+        )
+
+        const issuedSql = vi
+            .mocked(executeOperation)
+            .mock.calls.map((c) => (c[0] as any)[0].sql)
+        expect(issuedSql).toContain(
+            'SELECT * FROM users LIMIT 1000 OFFSET 0;'
+        )
+        expect(issuedSql).toContain(
+            'SELECT * FROM users LIMIT 1000 OFFSET 1000;'
+        )
+    })
+
+    it('should serialize NULL values as the NULL keyword', async () => {
+        vi.mocked(executeOperation)
+            .mockResolvedValueOnce([{ name: 'users' }])
+            .mockResolvedValueOnce([
+                { sql: 'CREATE TABLE users (id INTEGER, name TEXT);' },
+            ])
+            .mockResolvedValueOnce([{ id: 1, name: null }])
+
+        const response = await dumpDatabaseRoute(mockDataSource, mockConfig)
+        const dumpText = await response.text()
+
+        expect(dumpText).toContain('INSERT INTO users VALUES (1, NULL);')
+    })
+
     it('should return a 500 response when an error occurs', async () => {
         const consoleErrorMock = vi
             .spyOn(console, 'error')

src/export/dump.ts

@@ -3,67 +3,101 @@ import { StarbaseDBConfiguration } from '../handler'
 import { DataSource } from '../types'
 import { createResponse } from '../utils'
 
+// Number of rows fetched per page when dumping a table. Keeping this
+// bounded avoids loading entire tables into Worker memory, which is
+// what previously caused dumps of large databases to fail.
+const DUMP_PAGE_SIZE = 1000
+
+function formatValue(value: unknown): string {
+    if (value === null || value === undefined) return 'NULL'
+    if (typeof value === 'string') return `'${value.replace(/'/g, "''")}'`
+    return String(value)
+}
+
 export async function dumpDatabaseRoute(
     dataSource: DataSource,
     config: StarbaseDBConfiguration
 ): Promise<Response> {
     try {
-        // Get all table names
+        // Resolve the list of tables up front so any failure surfaces as a
+        // 500 (matching prior behavior) rather than mid-stream.
         const tablesResult = await executeOperation(
             [{ sql: "SELECT name FROM sqlite_master WHERE type='table';" }],
             dataSource,
             config
         )
-
         const tables = tablesResult.map((row: any) => row.name)
-        let dumpContent = 'SQLite format 3\0' // SQLite file header
 
-        // Iterate through all tables
-        for (const table of tables) {
-            // Get table schema
-            const schemaResult = await executeOperation(
-                [
-                    {
-                        sql: `SELECT sql FROM sqlite_master WHERE type='table' AND name='${table}';`,
-                    },
-                ],
-                dataSource,
-                config
-            )
+        const encoder = new TextEncoder()
+        const stream = new ReadableStream<Uint8Array>({
+            async start(controller) {
+                try {
+                    controller.enqueue(encoder.encode('SQLite format 3\0'))
 
-            if (schemaResult.length) {
-                const schema = schemaResult[0].sql
-                dumpContent += `\n-- Table: ${table}\n${schema};\n\n`
-            }
+                    for (const table of tables) {
+                        const schemaResult = await executeOperation(
+                            [
+                                {
+                                    sql: `SELECT sql FROM sqlite_master WHERE type='table' AND name='${table}';`,
+                                },
+                            ],
+                            dataSource,
+                            config
+                        )
 
-            // Get table data
-            const dataResult = await executeOperation(
-                [{ sql: `SELECT * FROM ${table};` }],
-                dataSource,
-                config
-            )
+                        if (schemaResult.length) {
+                            const schema = schemaResult[0].sql
+                            controller.enqueue(
+                                encoder.encode(
+                                    `\n-- Table: ${table}\n${schema};\n\n`
+                                )
+                            )
+                        }
 
-            for (const row of dataResult) {
-                const values = Object.values(row).map((value) =>
-                    typeof value === 'string'
-                        ? `'${value.replace(/'/g, "''")}'`
-                        : value
-                )
-                dumpContent += `INSERT INTO ${table} VALUES (${values.join(', ')});\n`
-            }
+                        // Page through the table so we never materialize the
+                        // full result set in memory.
+                        let offset = 0
+                        while (true) {
+                            const dataResult = await executeOperation(
+                                [
+                                    {
+                                        sql: `SELECT * FROM ${table} LIMIT ${DUMP_PAGE_SIZE} OFFSET ${offset};`,
+                                    },
+                                ],
+                                dataSource,
+                                config
+                            )
 
-            dumpContent += '\n'
-        }
+                            if (!dataResult.length) break
 
-        // Create a Blob from the dump content
-        const blob = new Blob([dumpContent], { type: 'application/x-sqlite3' })
+                            let chunk = ''
+                            for (const row of dataResult) {
+                                const values =
+                                    Object.values(row).map(formatValue)
+                                chunk += `INSERT INTO ${table} VALUES (${values.join(', ')});\n`
+                            }
+                            controller.enqueue(encoder.encode(chunk))
+
+                            if (dataResult.length < DUMP_PAGE_SIZE) break
+                            offset += DUMP_PAGE_SIZE
+                        }
+
+                        controller.enqueue(encoder.encode('\n'))
+                    }
+
+                    controller.close()
+                } catch (error) {
+                    controller.error(error)
+                }
+            },
+        })
 
         const headers = new Headers({
             'Content-Type': 'application/x-sqlite3',
             'Content-Disposition': 'attachment; filename="database_dump.sql"',
         })
 
-        return new Response(blob, { headers })
+        return new Response(stream, { headers })
     } catch (error: any) {
         console.error('Database Dump Error:', error)
         return createResponse(undefined, 'Failed to create database dump', 500)