Update the description about String 512MB limit

[hayashier]

512 MB max value limit was removed. redis/redis#757
proto-max-bulk-len was introduced with Redis 4.0.7. This limit seems to have been removed at that time.

Actually I confirmed I can set the strings, the size of which is over 512MB by changing proto-max-bulk-len and client-query-buffer-limit

So I updated this description.

[itamarhaber]

Hello @hayashier - thanks for this.

The 512MB limit has indeed been relaxed, but it is still the default behavior. To support bigger strings, one would first need to configure (proto-max-bulk-len directive) the server accordingly, so I'd rather have a clear explanation of that rather than deleting the relevant sentences.

Also, if you look through the docs, you'll find other references to the 512MB limit (e.g. SETBIT, SETRANGE and topics/protocol) so this would be a good chance to update all with this information.

[hayashier]

Hello itamarhaber,

I agree. I found the following parts which describe 512MB limit by using grep command.
And I agree we should explain about proto-max-bulk-len directive. I'll think about the updated idea.

1. https://redis.io/commands/client-setname

There is no limit to the length of the name that can be assigned if not the usual limits of the Redis string type (512 MB).

2. https://redis.io/commands/setbit

The offset argument is required to be greater than or equal to 0, and smaller than 232 (this limits bitmaps to 512MB). When the string at key is grown, added bits are set to 0.

On a 2010 MacBook Pro, setting bit number 232 -1 (512MB allocation) takes ~300ms, setting bit number 230 -1 (128MB allocation) takes ~80ms, setting bit number 228 -1 (32MB allocation) takes ~30ms and setting bit number 226 -1 (8MB allocation) takes ~8ms.

3. https://redis.io/commands/setrange

Note that the maximum offset that you can set is 229 -1 (536870911), as Redis Strings are limited to 512 megabytes. If you need to grow beyond this size, you can use multiple keys.

On a 2010 MacBook Pro, setting byte number 536870911 (512MB allocation) takes ~300ms, setting byte number 134217728 (128MB allocation) takes ~80ms, setting bit number 33554432 (32MB allocation) takes ~30ms and setting bit number 8388608 (8MB allocation) takes ~8ms.

4. https://redis.io/topics/data-types

A String value can be at max 512 Megabytes in length.

5. https://redis.io/topics/modules-api-ref

The function returns REDISMODULE_OK on success, and REDISMODULE_ERR on error, that is, the key is not open for writing, is not a string or resizing for more than 512 MB is requested.

6. https://redis.io/topics/protocol

Bulk Strings are used in order to represent a single binary safe string up to 512 MB in length.

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