How do you quickly iterate through a table with tens of thousands of records?

Exactly what the title says... I ran into a snag where a for in pairs isn't fast enough to check through tens of thousands of records (only does 60 per second). I need to check to see if a part's specific position is already inside a table so that when I generate another part from the user's input, the part will be placed in an area that has never been occupied.

I couldn't find any more information on something called maps and would appreciate some clarity as it may seem as though it could solve my problem.

Here is some quick code just to help show what I mean:

local myTable = {}
local part = game.Workspace.Part
local testerPart = game.Workspace.testerPart
local testPosition = Vector3.new(10,10,10)
local counter = 0
---- The following while loop is just to show you guys, I know they are all the same values
while counter < 1,000 do
    part:Clone()
    table.insert(myTable, part.Position)
    counter = counter + 1
end

---- This part is just too slow
for i, v in pairs(myTable) do
    if v == testPosition then
        break -- since it's already inside the table
    elseif i = #myTable then      ---if it reached the last record without finding a match
        testerPart:Clone()       ----then copy the testerPart
        testerPart.Parent = game.Workspace       --- parent it to Workspace
        testerPart.Position = testPosition       -- give it the position
    end

end