>Please suggest to improve performance as it is high traffice e-commerce site and it goes down when MySQL has 1500 connections on each server.
Looking at your per-thread memory usage:
| query_cache_size | 536870912 | #512M
| sort_buffer_size | 33554432 | #32M
| read_buffer_size | 8388608 | #8M
| join_buffer_size | 8388608 | #8M
| tmp_table_size | 134217728 | #128M
| max_heap_table_size | 16777216 | #16M
| thread_stack | 262144 | #256K
So if we calcualte total memory required to support 1500 connections, it will be 23G RAM. How much RAM do you have?
Can you provide us SHOW GLOBAL STATUS output for a review?
Recommended values for the above per-thread memory buffers:
sort_buffer_size = 131072 # leave to default
query_cache_size = 50M # I would like to see output of SHOW GLOBAL STATUS first.
read_buffer_size = 131072 # default is ok
Good readings:
http://www.mysqlperformanceblog.com/2010/10/25/impact-of-the-sort-buffer-size-in-mysql/
http://www.mysqlperformanceblog.com/2007/09/17/mysql-what-read_buffer_size-value-is-optimal/