A message is a distinct piece of information transmitted by one client that can be received by one or more other clients. Each SQS message is identified by an ID value generated by the service. A message’s ID uniquely identifies that message within a queue, and the combination of a queue URL and a message ID can uniquely identify any message in SQS.
There is no limit to the number of messages that can be sent to SQS queues, nor to the number that may remain stored in queues pending delivery. Messages cannot be left in the service indefinitely; they will be automatically deleted after 15 days or so.
SQS does not include a timestamp with messages to indicate when a particular message was sent. This makes it difficult to check whether your queues contain messages that are nearly 15 days old. SQS is not intended for long-term data storage, so you must be prepared for very old messages to be deleted.
Messages have a maximum size of 256 KB. This size limit is not large by the standards of alternative messaging systems, and it clearly indicates Amazon’s intentions for how its messaging service should be used. SQS is not intended to serve as a means for distributing files or transmitting large data objects; it is intended to carry short notifications or instruction messages that refer to data resources stored outside the SQS service, for example, in the Simple Storage Service (S3).
The data content of SQS messages must be unicode text characters that are legal for standard XML ...