Chapter 7. Reading Table Rows

Table of Contents

Read Exceptions
Retrieving a Single Row
Retrieve a Child Table
Using multiGet()
Iterating over Table Rows
Specifying Field Ranges
Using MultiRowOptions to Retrieve Nested Tables
Reading Indexes
Parallel Scans

There are several ways to retrieve table rows from the store. You can:

  1. Retrieve a single row at a time using TableAPI.get().

  2. Retrieve rows associated with a shard key (which is based on at least part of your primary keys) using either TableAPI.multiGet() or TableAPI.multiGetIterator().

  3. Retrieve table rows that share a shard key, or an index key, using TableAPI.tableIterator().

Each of these are described in the following sections.

Read Exceptions

One of three exceptions can occur when you attempt a read operation in the store. The first of these is ConsistencyException. This exception indicates that the operation cannot be completed because the consistency policy cannot be met. For more information, see Consistency Guarantees.

The second exception is RequestTimeoutException. This means that the operation could not be completed within the amount of time provided by the store's timeout property. This probably indicates a store that is attempting to service too many read requests all at once. Remember that your data is partitioned across the shards in your store, with the partitioning occurring based on your shard keys. If you designed your keys such that a large number of read requests are occurring against a single key, you could see request timeouts even if some of the shards in your store are idle.

A request timeout could also be indicative of a network problem that is causing the network to be slow or even completely unresponsive.

To handle a RequestTimeoutException, you could simply log the error and move on, or you could pause for a short period of time and then retry the operation. You could also retry the operation, but use a longer timeout value.

Finally, you can receive a general FaultException, which indicates that some exception occurred which is neither a problem with consistency nor a problem with the request timeout. Your only recourse here is to either log the error and move along, or retry the operation.