I am trying to understand subscriber and publisher buffers. If I set subsrciber buffer to 1000 and publisher buffer to 1, are there any chances that I loose messages ? Could anyone please explain me the same?
Yes, in theory you may lose messages with these settings, in practice it depends.
Theory: spinner threads
On both sides, publisher as well as subscriber, there are so called spinner threads responsible for handling the callbacks (for message sending on the publisher side and message evaluation on the subscriber-side). These spinner threads are working in parallel to the main thread. If messages are arriving faster from the main thread than they are being processed by the spinner thread, the number of messages given by the queue size will be buffered up before beginning to throw away the oldest ones. Therefore if you publish at a very high rate the publisher-sided spinner thread might drop older messages, while if your callback function on the subscriber side takes too long to execute your subscriber queue will start dropping messages. To improve this one can use multi-threaded spinners where one increases the number of spinner threads and activate concurrency in order to process the callback queue more quickly. Read more about it here.
Practice: Choosing the queue size
The queue size of the publisher queue you should set depends on which rate you publish and if you publish in bursts. If you publish in bursts or at higher frequencies (e.g. > 10 Hz) a publisher queue size of 1 won't be sufficient. On the subscriber side it is harder to give recommendations as it also depends on how long the callback takes to process the information.
It is actually also possible to set the value 0 for the queues which results in an arbitrarily large queue but this might be problematic as the required memory might grow indefinitely, well at least until your computer freezes. Furthermore having a large queue size might often be disadvantageous: If you set a large queue and the callback takes long to execute you might be working on very outdated data while the queue gets longer and longer.
Alternative communication patterns
If you want to guarantee that information is actually being processed (e.g. real-time or safety-relevant information) ROS topics are probably the wrong choice. Depending on what precisely you need the other two communication methods services or actions might be an alternative. But for things like large information streams of safety-relevant real-time data there are no perfect communication mechanisms in ROS1.