javascript - Most suitable pushing technique for specific operation -

i have website in php , i'm trying implement push notification system handles following:

1) data array other website's api 2) check if data exists in own mysql database 3) if of them doesn't, send new notification client including these data 4) else go step 1

i've used ajax comet technique achieve this, wondering if it's going slow when dealing lets 500 users doing requests database. caching way 1 follow then?

generally speaking, there better approach problem using comet technique? asking guidance, not specific implementations.

thanks lot!