Mysql – Realtime Update MySQL on every Update occurred on PostgreSQL

You'll need to either use an ETL Tool eg Microsoft SSIS. There's plenty of open source products available too. Or you can build your own extract utility using a programming language like PHP, .Net etc.

The Kimball guys have an article on whether you should build your own or use an off the shelf product. http://www.kimballgroup.com/2008/04/should-you-use-an-etl-tool/

To schedule the load, you can use windows scheduler on Windows or cron jobs on Unix.

Yes you can do that. The easiest way to do if your amount of rows is relatively small is:

update vertex set name = 'CCCC' 
where latitude between 6.9271786 * 0.99 and 6.9271786 * 1.01 and 
      longitude between 79.86224300000006 * 0.99 and 79.86224300000006 * 1.01;

With of course setting your threshold to the right level. The above example assumes 1% which is huge in terms of geo coordinates but you get the idea.

Since MySQL can only use one column for range queries from a composite key having a combined index won't help but separate index on latitude and longitude will. Then MySQL can choose the one which is more distinctive for the specific case.

create index lat_idx on vertex (latitude);
create index lat_idx on vertex (longitude);

For further optimizations if necessary you can look into spatial indexes (you haven't mentioned which MySQL version and engine you're using).

Also you can geohash the coordinates into a single numerical column and have proximity match on that then filter by the coordinates which I use on bigger database and works like a charm.

https://en.wikipedia.org/wiki/Z-order_curve https://en.wikipedia.org/wiki/Geohash