[Sqlalchemy-tickets] Issue #3931: Memory leak on creating savepoints (zzzeek/sqlalchemy)

[Bartłomiej B. <iss...@bi...>]

New issue 3931: Memory leak on creating savepoints
https://bitbucket.org/zzzeek/sqlalchemy/issues/3931/memory-leak-on-creating-savepoints

Bartłomiej Biernacki:

I found a small memory leak when using many savepoints to the same DB.

Consider this code example:

```
#!python

session = create_session()

for _ in range(0, 5000):
    session.begin_nested()
    session.execute(
        sa.insert(Test).values(name='test'))
    session.commit()

session.commit()
session.close()
```

After this we can observe 5000 strings with savepoints names in memory. 

Diging deeply into it I found that function `sql/compiler.py:format_savepoint` saves savepoint name to `self._strings`. By default savepoint names are unique for each nested transaction so saving them for future use is redundant and each new savepoint name stays in memory.

My proposition is to change the function, so savepoint name won't be saved:

```
#!python

    def format_savepoint(self, savepoint, name=None):
        value = name or savepoint.ident
        if self._requires_quotes(value):
            return self.quote_identifier(value)
        return value
```

Complete code example for reproducing bug in attachment.