Question:

What is Salesforce Bulk API? What are Serial and Parallel Modes in the Salesforce Bulk API Feature?

Answer:

Review the Salesforce page:  Salesforce Integration Tips: Using the Bulk API - Serial or Parallel mode options.

To configure Data Loader to use the Bulk API for inserting, updating, upserting, deleting, and hard deleting records:

1. Open the Data Loader.
2. Choose Settings | Settings.
3. Select the Use Bulk API option.
4. Click OK. 

Bulk API modes which are also referred to as Concurrency modes are as follows:

• 1. Parallel mode
  
  This is the default mode in the Bulk API. Salesforce will process all the batches in a posted job in parallel and this gives a better performance in uploading data. However, this might lead to lock contention which will cause the upload to fail.

• 2. Serial mode
  
  Salesforce processes all the batches in a posted job one by one and this can help to prevent the lock contention issue that can be encountered in Parallel mode.

Related Documentation:

Salesforce Help Documentation:

• Configure the Data Loader to Use the Bulk API

Third Party Documentation:

• Salesforce Integration Tips: Using the Bulk API – Serial or Parallel mode options

Knowledge Base:

• Does Salesforce Support Dataloader, Workbench, Salesforce Inspector?