Package lmdb-0.9.29 was installed; and py-lmdb, as a --user install, from PyPi
so lmdb can be used from Python3.9.
Behaviour seemed erratic, including segmentation faults, but for a while it
seemed possible to avoid these by using alternative methods supported by
py-lmdb.
Eventually I got stuck and downloaded the project from
github.com/jnwatson/py-lmdb/ to try running the address-book example and modify
it toward something like the problem case at which I was stuck.
Running got a segmentation fault immediately but repeated retries after
deleting the *.sem siblings of /tmp/address-book.lmdb got to a case where the
run did not give a segmentation fault.
The first script below shows this and includes a list of installed packages and
dmesg output.
The second script below is from an equivalent FreeBSD session and shows the
address-book example giving the expected output.
I was assuming py-lmdb should just work, but notice FreeBSD has a port but not
OpenBSD: so maybe assumption is wrong?
Script started on Sat Jan 28 12:59:27 2023
opendev$ uname -a
OpenBSD opendev.home 7.2 GENERIC.MP#758 amd64
opendev$ ls /tmp
sndio vi.recover
opendev$ python3.9 py-lmdb-py-lmdb_1.4.0/examples/address-book.py
Segmentation fault (core dumped)
opendev$ ls /y tmp
2192baec8c73f403a857cb5e31a384a8481d96ab965510ec63ad71da9798c522.sem
address-book.lmdb
eebfd9cc55a9dc2ab5b13550e78544804307f93944815b7760405d5dfeac1b0f.sem
sndio
vi.recover
opendev$ python3.9 py-lmdb-py-lmdb_1.4.0/examples/address-book.py
Segmentation fault (core dumped)
opendev$ ls /tmp/*.sem
/tmp/2192baec8c73f403a857cb5e31a384a8481d96ab965510ec63ad71da9798c522.sem
/tmp/eebfd9cc55a9dc2ab5b13550e78544804307f93944815b7760405d5dfeac1b0f.sem
opendev$
opendev$ ls /tmp/*.sem /tmp/*.sem /tmp/*.sem
r /tmp/*.semm /tmp/*.sem
opendev$
opendev$ rm /tmp/*.sem
opendev$ ls /tmp/*.sem
opendev$ python3.9 py-lmdb-py-lmdb_1.4.0/examples/address-book.py
DB: home
DB: business
Updating number for dentist
Segmentation fault (core dumped)
opendev$
opendev$ python3.9 py-lmdb-py-lmdb_1.4.0/examples/address-book.py
opendev$ rm /tmp/*.sem
opendev$
opendev$ rm /tmp/*.sem
opendev$ python3.9 py-lmdb-py-lmdb_1.4.0/examples/address-book.py
DB: home
DB: business
Updating number for dentist
Deleting number for hospital
Home DB is now:
b'dentist' b'01231'
Boss telephone number: b'0123151232'
Deleting all numbers from business DB:
Adding number for recruiter to business DB
Business DB is now:
b'recruiter' b'04123125324'
opendev$ ls /tmp
address-book.lmdb sndio vi.recover
opendev$
opendev$
opendev$ ls /tmp
opendev$ python3.9 py-lmdb-py-lmdb_1.4.0/examples/address-book.py
DB: home
b'recruiter' b'04123125324'
DB: business
Updating number for dentist
Deleting number for hospital
Home DB is now:
b'dentist' b'01231'
b'recruiter' b'04123125324'
Boss telephone number: None
Deleting all numbers from business DB:
Adding number for recruiter to business DB
Business DB is now:
b'recruiter' b'04123125324'
opendev$
opendev$ python3.9 py-lmdb-py-lmdb_1.4.0/examples/address-book.py
opendev$ ls /tmp
address-book.lmdb sndio vi.recover
opendev$
opendev$ cat py-lmdb-py-lmdb_1.4.0/examples/address-book.py
import lmdb
# Open (and create if necessary) our database environment. Must specify
# max_dbs=... since we're opening subdbs.
env = lmdb.open('/tmp/address-book.lmdb', max_dbs=10)
# Now create subdbs for home and business addresses.
home_db = env.open_db(b'home')
business_db = env.open_db(b'business')
# Add some telephone numbers to each DB:
with env.begin(write=True) as txn:
txn.put(b'mum', b'012345678', db=home_db)
txn.put(b'dad', b'011232211', db=home_db)
txn.put(b'dentist', b'044415121', db=home_db)
txn.put(b'hospital', b'078126321', db=home_db)
txn.put(b'vendor', b'0917465628', db=business_db)
txn.put(b'customer', b'0553211232', db=business_db)
txn.put(b'coworker', b'0147652935', db=business_db)
txn.put(b'boss', b'0123151232', db=business_db)
txn.put(b'manager', b'0644810485', db=business_db)
# Iterate each DB to show the keys are sorted:
with env.begin() as txn:
for name, db in ('home', home_db), ('business', business_db):
print('DB:', name)
for key, value in txn.cursor(db=db):
print(' ', key, value)
print()
# Now let's update some phone numbers. We can specify the default subdb when
# starting the transaction, rather than pass it in every time:
with env.begin(write=True, db=home_db) as txn:
print('Updating number for dentist')
txn.put(b'dentist', b'01231')
print('Deleting number for hospital')
txn.delete(b'hospital')
print()
