About the `next_short_code` function about pygmy

[amitt001]

@Hu1-Li I see where this issue is coming from. Ordering the links by created_at desc and then picking the top link as latest will cause this. As for high load websites with many concurrent requests at a time will have many rows with the same created_at time. Wrong ordering is causing while loop and eventually select queries in MySQL to execute many more times than expected.

This can be fixed by ordering by id instead of created_at in latest_default_link method.

I am bit busy right now, I will fix and test this when I get some time. Would you like to make necessary changes and the above tests and open a PR?

[Hu1-Li]

OK, I will try.

[Hu1-Li]

Update:
[USING MYSQL]
In my test on the fixed code, which change ordering from created_at to id, the test comes with A99, then it got stucks. As expect, the next short code should be Baa, as the below line

link_manager.find(short_code=base_str)

it got baa

In Mysql, String compare is case-insensitive, thus, causing the server down ,since it needs to loop a really big cycle, from baa to A99 then starts over and over again.

So when creating table, the field short_code should be

short_code varchar(10) COLLATE utf8_bin DEFAULT NULL,`

In SQLAchemy, This can be achieved by

short_code = Column(Unicode(6, collation="utf8_bin"), unique=True, index=True, default=None)

[Hu1-Li]

Pull request #17 fixes this problem, As for test, i get no idea how to achieve the test for the above problem @amitt001

// Update
For sqlite, it should be
Column(Unicode(6, collation="BINARY"), unique=True, index=True, default=None)
For mysql, it should be
Column(Unicode(6, collation="utf8_bin"), unique=True, index=True, default=None)

emmmm,

[amitt001]

Fixed in commit: 67260ba

@Hu1-Li Thanks for fixing this bug and contributing 🍰