Excessive memory use or memory fragmentation when unpickling many small objects

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-04-21.17:11:20.009>
labels = ['3.8', 'library', 'performance']
title = 'Excessive memory use or memory fragmentation when unpickling many small objects'
updated_at = <Date 2019-05-02.16:43:18.896>
user = 'https://github.com/Paul-E'

bugs.python.org fields:

activity = <Date 2019-05-02.16:43:18.896>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-04-21.17:11:20.009>
creator = 'Ellenbogen'
dependencies = []
files = ['48279', '48280', '48282']
hgrepos = []
issue_num = 36694
keywords = ['patch']
message_count = 8.0
messages = ['340615', '340616', '340617', '341179', '341181', '341193', '341251', '341284']
nosy_count = 5.0
nosy_names = ['pitrou', 'alexandre.vassalotti', 'methane', 'serhiy.storchaka', 'Ellenbogen']
pr_nums = ['13036']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'resource usage'
url = 'https://bugs.python.org/issue36694'
versions = ['Python 3.8']