Postgres MCP Server

Instructions

Implementation Reference

• src/index.ts:285-317 (schema)

  Schema definition for the 'transactions' MCP tool, including input parameters and actions (begin, commit, rollback, status, etc.)
  { name: 'transactions', description: 'Transaction management: begin, commit, rollback, savepoints', inputSchema: { type: 'object', properties: { action: { type: 'string', enum: ['begin', 'commit', 'rollback', 'savepoint', 'rollback_to', 'release', 'status'], description: 'Action: begin (start transaction), commit (commit transaction), rollback (rollback transaction), savepoint (create savepoint), rollback_to (rollback to savepoint), release (release savepoint), status (transaction status)' }, transactionId: { type: 'string', description: 'Transaction ID (required for commit, rollback, and operations within transaction)' }, savepointName: { type: 'string', description: 'Savepoint name (required for savepoint, rollback_to, release)' }, readOnly: { type: 'boolean', description: 'Start read-only transaction (for begin action)', default: false }, isolationLevel: { type: 'string', enum: ['READ UNCOMMITTED', 'READ COMMITTED', 'REPEATABLE READ', 'SERIALIZABLE'], description: 'Transaction isolation level (for begin action)' } }, required: ['action'] } },
• src/index.ts:634-637 (registration)

  Registration of the 'transactions' tool via the toolDefinitions array returned in ListToolsRequestSchema handler
  this.server.setRequestHandler(ListToolsRequestSchema, async () => ({ tools: toolDefinitions, }));
• src/index.ts:1082-1126 (handler)

  Primary handler function for 'transactions' tool calls, handling begin/commit/rollback/status actions by delegating to DatabaseConnectionManager
  private async handleTransactions(args: any) { const { action, transactionId, readOnly, isolationLevel } = args; switch (action) { case 'begin': const txId = await this.dbManager.beginTransaction(readOnly); return { content: [{ type: 'text', text: JSON.stringify({ transactionId: txId, status: 'started' }, null, 2) }] }; case 'commit': ParameterValidator.validateRequired(transactionId, 'transactionId'); await this.dbManager.commitTransaction(transactionId); return { content: [{ type: 'text', text: JSON.stringify({ transactionId, status: 'committed' }, null, 2) }] }; case 'rollback': ParameterValidator.validateRequired(transactionId, 'transactionId'); await this.dbManager.rollbackTransaction(transactionId); return { content: [{ type: 'text', text: JSON.stringify({ transactionId, status: 'rolled_back' }, null, 2) }] }; case 'status': return { content: [{ type: 'text', text: JSON.stringify(this.dbManager.getOperationalStats(), null, 2) }] }; default: throw new Error(`Unknown transaction action: ${action}`); } }
• src/database/connection-manager.ts:158-193 (helper)

  Core beginTransaction helper method that creates a new transaction context, supports read-only mode, and tracks active transactions
  async beginTransaction(readOnly: boolean = false): Promise<string> { const transactionId = uuidv4(); const client = await this.pool.connect(); try { if (readOnly) { await client.query('BEGIN READ ONLY'); } else { if (this.config.isReadOnlyMode()) { throw new Error('Write transactions are not allowed in read-only mode'); } await client.query('BEGIN'); } const context: TransactionContext = { id: transactionId, client, startTime: Date.now(), readOnly }; this.activeTransactions.set(transactionId, context); this.connectionStats.totalTransactions++; logConnection('transaction_started', { transactionId, readOnly, activeTransactions: this.activeTransactions.size }); return transactionId; } catch (error) { client.release(); throw error; } }
• src/database/connection-manager.ts:235-253 (helper)

  Core commitTransaction helper method that commits the transaction and cleans up the context
  async commitTransaction(transactionId: string): Promise<void> { const context = this.activeTransactions.get(transactionId); if (!context) { throw new Error(`Transaction ${transactionId} not found`); } try { await context.client.query('COMMIT'); const duration = Date.now() - context.startTime; logConnection('transaction_committed', { transactionId, duration: `${duration}ms` }); } finally { context.client.release(); this.activeTransactions.delete(transactionId); } }
• src/database/connection-manager.ts:258-276 (helper)

  Core rollbackTransaction helper method that rolls back the transaction and cleans up the context
  async rollbackTransaction(transactionId: string): Promise<void> { const context = this.activeTransactions.get(transactionId); if (!context) { throw new Error(`Transaction ${transactionId} not found`); } try { await context.client.query('ROLLBACK'); const duration = Date.now() - context.startTime; logConnection('transaction_rolled_back', { transactionId, duration: `${duration}ms` }); } finally { context.client.release(); this.activeTransactions.delete(transactionId); } }
• src/database/connection-manager.ts:297-302 (helper)

  getOperationalStats helper method providing transaction status and statistics used by 'status' action
  getOperationalStats() { return { ...this.connectionStats, activeTransactions: this.activeTransactions.size, poolStats: this.getPoolStats() };