I am trying to set Use Flat Catalog Product = Yes but if i reindex store than it shows below error.
SQLSTATE: Syntax error or access violation:1118 Row size too large. The Maximum row size for the used table type, not counting BLOBs, is 65535. This includes storage overhead, check the manual. You have to change some columns to TEXT or BLOBs, query was: CREATE TEMPORARY TABLE `catalog_product_entity_varchar_tmp_indexer`()
I am using Magento 2.1.5 version.
Thanks for your answer in advance.
Most probably you have many attributes. Each attribute is varchar(255) so it's easy to reach the 64K limit.
Try changing some attributes and disabling "used in product listing" and sorting, to remove them from flat catalog product table.
Then try reindexing again.