**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 :)

{
}
PartitionCommandsResultInfo MergeTreeData::unfreezePartition(
    const ASTPtr & partition,
    const String & backup_name,
    ContextPtr local_context,
    TableLockHolder &)
{
    return unfreezePartitionsByMatcher(getPartitionMatcher(partition, local_context), backup_name, local_context);
}
PartitionCommandsResultInfo MergeTreeData::unfreezeAll(
    const String & backup_name,
    ContextPtr local_context,
    TableLockHolder &)
{
    return unfreezePartitionsByMatcher([] (const String &) { return true; }, backup_name, local_context);
}
bool MergeTreeData::removeDetachedPart(DiskPtr disk, const String & path, const String &, bool)