While using hash partition i am facing the problem that the data is not going into the proper partition table . Due to this, records are not visible in the main table when I am searching for a particular record, as it searches only that partition. Any suggestions on how to overcome this problem and why this happened.
This seems like a bug, or some kind of corruption. But there isn't enough info here to identify what the bug might be. Are you using a custom hashing function, or a built-in one? What is the datatype of the partition key? Has this system been through any pg_upgrade cycles? Have you tried to reproduce it on your own system? What is your version and hardware and OS? Do you have error correcting code RAM?
And in the future, if i truncate the records from the main table and insert them back again, will the shuffling of records happen or not. Any ideas regarding why this happened?
I don't think there is a way to answer that without first identifying what went wrong in the first place.