I read some where that Zerodha OMS have some limitation eg like 15K orders per sec. This is the reason Day orders take some time to get filled even if they are at the limit price.
I have tried IOC orders but almost 90% of the time IOC didnt get filled. We might need IOC orders if we are trading in a scenaio where we want the enter the position immediately not wait like in a Day Validity order.
Just wondering if IOC have any precedence over other day orders.
IOC orders have no priority over Day validity orders. An IOC order is an immediate or cancel order, implying that as soon as you place this order, it will immediately execute if there is a matching counter order or it will be cancelled if there is no matching counter order.
If you place an IOC Buy Limit order say with price = 100 and if there is a seller available at 100 when your order is open at the exchange, then your order will execute and if there is no seller at this price, then the order will cancel. Your IOC orders could be partially filled too if a seller of a lesser quantity is available at your price when the order is open and the rest of the unfilled quantity will be immediately cancelled.
This is the reason why your IOC orders cancel 90% of the times, the chances of it getting executed immediately are very slim. It has nothing to do with the OMS.
You could place market orders to ensure that your orders are always executed. But if you place market orders with larger quantities, then there is a high chance that all sellers will not be available at the same price and your order might fill at higher prices where sellers are available.
To ensure your entire order is executed at the same price, there is always a limit order. But this need not necessarily be immediate.