Order By Clause, Slows Query Performance?

Eg. SELECT col1, col2, col3,....col10 FROM table1;

For above query If I didn't mention ORDER BY clause, then I want to know
selected data will appear in which order by a query planner?

Because I have huge size table, and when I applied ORDER BY col1, col2..in
query the
performance is soo bad that I can't offred.
What should I do ? Because my requirement is data with ordered column.

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