Add memory size estimation for ParquetMetadata

[alamb]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
In https://github.com/influxdata/influxdb_iox, caching is very important to performance. Part of what is cached in memory is a ParquetMetadata structure. In order to effectively cache this data (and free it when under memory pressure) we need to know an accurate estimate of the heap it is using.

Describe the solution you'd like
I would like a function such as the following that accurately estimates the memory usage of parquet metadata:

impl ParquetMetadata {
    ...

    /// In-memory size in bytes, including `self`.
    pub fn size(&self) -> usize {
        // recursively 
    }

   ...
}

Describe alternatives you've considered
I believe @domodwyer is considering caching only the parts that we need (rather than the ParquetMetadata object itself) in which case we would likely not need this feature in IOx. I think it would still be generally helpful though

Additional context
See https://github.com/influxdata/influxdb_iox/pull/4661 for example of usecase

[alamb]

I believe @crepererum may be working on this

[crepererum]

I think I might not. After a quick look at the data structures, the memory estimation is quite a mess, especially for the parquet schema data.

[alamb]

I am going to try and find time to do this sometime this week

[Xuanwo]

In https://github.com/influxdata/influxdb_iox, caching is very important to performance. Part of what is cached in memory is a ParquetMetadata structure.

Seems a typo here, https://github.com/influxdata/influxdb_iox is empty

[Xuanwo]

Oh, I see. This issue created in 2022, and influxdb_iox has been renamed to influxdb. What a history!

[alamb]

Oh, I see. This issue created in 2022, and influxdb_iox has been renamed to influxdb. What a history!

Yeah, the actual history is more tortured -- if you care it is here https://www.influxdata.com/blog/the-plan-for-influxdb-3-0-open-source/

TLDR is that we made the influxdb_iox repo private

[alamb]

Here is a proposed PR with a fix: #5965