What's the best way to reuse large map

[Zhang,Lei(Ecom)]

I need use a very large map in a function and the function will be repeatedly called many times.

At the beginning of the function, the map need be empty.

One way to do it is to use/reuse just one permanent map object and clear it at the beginning of the function.

Another way is to create a new map object in the function.

Since the map is very large, I'd like to save some memory and keep the burden on GC low.

So I guess the first way is preferred. But I am not sure whether clearing a map and reusing it is really memory-efficient

compared to creating a new map object in each call. It depends on how map is implemented internally.

 

Any ideas and suggestions ?

 

Thanks !

 

Zhang Lei

Baidu, Inc.

 

 

 

[Andrew Gerrand]

The best approach for you depends on many factors. The best way to find out is to try re-allocating vs re-using a map and profiling the performance. 

http://blog.golang.org/profiling-go-programs

Andrew

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[Caleb Spare]

Note that "clearing" a map means iterating through it and deleting the
entries one-by-one.

Also note that you can give a map a size hint: make(map[X]Y, 10000).
That way the map may be pre-sized and will hopefully do fewer
allocations/copying as it grows.

You could use the previous map size to know how large to hint in the
next iteration, for example.

If I were you, I would compare these two approaches:

1. Clear the map between each iteration
2. Throw away the map each iteration but use its size as a hint for
making the new map

Writing a benchmark is the best way to see what's going to happen in
your particular situation. I would expect that #2 is the fastest.

-Caleb

[Daniel Mal]

i asked this once, see

https://groups.google.com/forum/#!topic/golang-nuts/UvUm3LA1u8g