please suggest if there is any way which i can find which tables need indexes in postgresql.
You have some possibilities:
- the log file (slow queries)
- statistics with old information (see the ANALYZE command)
- statistics tables, for example: pg_stat_user_tables
You can run this SQL:
SELECT pg_stat_user_tables.schemaname, pg_stat_user_tables.relname, pg_stat_user_tables.seq_scan, pg_stat_user_tables.seq_tup_read, pg_stat_user_tables.idx_scan, pg_stat_user_tables.idx_tup_fetch FROM pg_stat_user_tables;
If you have a big value in seq_scan column compared to the idx_scan column (small value), this indicate that you probably need to create an index in some column, but you need to discover what column needs the index. (the log file is a good indication).
I'll also give a shout-out for pgBadger. It parses your slow query logs and creates a nice summary of queries that could use some attention.