**Describe the bug**

Since we upgraded to 20.10.3.30, one of our clickhouse cluster takes much more time to start. (Up to 50 minutes, and before it took ~3 minutes)
The log file is filled with
>  <Debug> DiskLocal: Reserving 1.00 MiB on disk `default`, having unreserved 16.90 TiB

Additionally, the memory consumption increases, linearly, a lot (up to arround 230 G for us) and then drop back to normal values once clickhouse finished starting up. During that loading phase, a single CPU core is used at 100%.
If that memory is not available for the machine, clickhouse gets OOMed by the kernel.


**How to reproduce**
* Issue appeared after we upgraded to ClickHouse server version 20.10.3.30

* How could I find wich of our tables may be responsible for that ?


**Expected behavior**
A fast startup :)

#include <typeindex>
#include <unordered_set>
#include <filesystem>
namespace fs = std::filesystem;
namespace ProfileEvents
{
    extern const Event RejectedInserts;
    extern const Event DelayedInserts;
    extern const Event DelayedInsertsMilliseconds;
    extern const Event InsertedWideParts;
    extern const Event InsertedCompactParts;
    extern const Event InsertedInMemoryParts;
    extern const Event MergedIntoWideParts;
    extern const Event MergedIntoCompactParts;
    extern const Event MergedIntoInMemoryParts;
}
namespace CurrentMetrics
{
    extern const Metric DelayedInserts;
}
namespace
{
    constexpr UInt64 RESERVATION_MIN_ESTIMATION_SIZE = 1u * 1024u * 1024u; 
}
namespace DB
{
namespace ErrorCodes
{
    extern const int NO_SUCH_DATA_PART;
    extern const int NOT_IMPLEMENTED;