**Summary**
After upgrading a host that is just a collection `Distributed` tables to 20.4.X and 20.5.2.7, we observe the new `MemoryTracking` setting increasing substantially during writes, leading to individual writes and reads yielding exceptions: ```Memory limit (total) exceeded: would use 28.28 GiB (attempt to allocate chunk of 4197840 bytes), maximum: 28.28```

System metrics show that no actual memory is being allocated to the same size.
<img width="993" alt="Screen Shot 2020-07-19 at 12 23 59 PM" src="https://user-images.githubusercontent.com/1189446/87883721-229e7280-c9be-11ea-851b-0e1511cc10bb.png">

Please let me know if there is any additional context, diagrams, or statements I should provide. I'm interested in knowing how to correlate the total `MemoryTracking` metric to anything else since system memory does not reflect the metric at all.

**Context**
This host has four different `Distributed` tables that are written to via the HTTP interface with `insert_distributed_sync=1` set.
The host itself has no local tables.

The hosts with the downstream local tables are all 20.5.2.7.

We have downgraded the `Distributed` host in question back to 20.3.9.70 in order to continue writing to the clusters.
#pragma once
#include <DataStreams/IBlockInputStream.h>
#include <Formats/FormatFactory.h>
#include <Common/ThreadPool.h>
#include <Common/setThreadName.h>
#include <IO/BufferWithOwnMemory.h>
#include <IO/ReadBuffer.h>
#include <Processors/Formats/IRowInputFormat.h>
#include <Processors/Formats/InputStreamFromInputFormat.h>
namespace DB
{
/**
 * ORDER-PRESERVING parallel parsing of data formats.
 * It splits original data into chunks. Then each chunk is parsed by different thread.
 * The number of chunks equals to the number or parser threads.
 * The size of chunk is equal to min_chunk_bytes_for_parallel_parsing setting.