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Comment by logicchains | Hacker News Reader

One issue is that the server uses Google Protocol Buffers. The following definition, for instance:

    message Foo {
	required string a = 1;
	required int32 b = 2;
	optional int64 c = 3;
    }

Generates a struct like:

    type Foo struct {
        a *string
        b *int32
        c *int64
    }

This is not particularly friendly to the garbage collector compared to a POD struct with no pointers.

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Protocol buffers allows you to reuse the memory of your objects. You can simply reuse the object where you parse your message into. You pool these objects, and you just saved yourself a huge amount of heap allocations.

https://developers.google.com/protocol-buffers/docs/referenc...

This would work if we were only using them for messaging, but the protobuffer objects are also used as the datastructure in which the information they contain is stored. This was done in the name of simplicity, to avoid creating a separate internal datastructure for each kind of message.

The flow of data is currently:

various external sources -> merged into protocol buffer struct -> later sent to client

To avoid keeping a heap of protocol buffer structs in the heap, this would need to change to:

various external sources -> merged into some internal datastructure -> later converted into protocol buffer struct and sent to client.

> This would work if we were only using them for messaging, but the protobuffer objects are also used as the datastructure in which the information they contain is stored. This was done in the name of simplicity, to avoid creating a separate internal datastructure for each kind of message.

Did you consider keeping strings (serialized messages) in your cache rather than message objects? I do this in C++ code simply for memory efficiency. Here it would also allow you to avoid these extra pointers.

FYI, if you don't need required/optional, non-zero defaults and extensions, try `syntax = "proto3"`. It generates much better Go code.

How can you have a POD struct without pointers if one of your fields is a string?

Couldn't it be done with a fixed-size array of runes or bytes? It's definitely possible in C/C++.

Not without wasting a lot of space depending on the difference between average size of string vs maximum size of string.

We generally know the maximum string sizes for each property, and they're pretty small, so this wouldn't have been a problem.

You can use a string class like the one in Folly that decays from a fixed array to heap allocated space if the string gets too long.

I believe it's also possible to use variable-size arrays in C or C++ (and end up with a variable-size struct).

Go does allow fixed size arrays in structs, and they're inline in the struct, so `struct { foo [8]uint }` is 32 bytes, whereas `struct { foo []uint }` is 12 bytes and `struct { foo string }` is 8.

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