问题
在跑 OpenStack functional 功能测试的时候有两个用例过不去。
- nova.tests.functional.db.test_resource_provider.ResourceClassTestCase.test_create_duplicate_id_retry
- nova.tests.functional.db.test_resource_provider.ResourceClassTestCase.test_create_duplicate_id_retry_failing
调试定位到问题代码：
# /opt/stack/queens/nova/nova/objects/resource_provider.py
def create(self):
if 'id' in self:
raise exception.ObjectActionError(action='create',
reason='already created')
if 'name' not in self:
raise exception.ObjectActionError(action='create',
reason='name is required')
if self.name in fields.ResourceClass.STANDARD:
raise exception.ResourceClassExists(resource_class=self.name)
if not self.name.startswith(fields.ResourceClass.CUSTOM_NAMESPACE):
raise exception.ObjectActionError(
action='create',
reason='name must start with ' +
fields.ResourceClass.CUSTOM_NAMESPACE)
updates = self.obj_get_changes()
# There is the possibility of a race when adding resource classes, as
# the ID is generated locally. This loop catches that exception, and
# retries until either it succeeds, or a different exception is
# encountered.
retries = self.RESOURCE_CREATE_RETRY_COUNT
while retries:
retries -= 1
try:
rc = self._create_in_db(self._context, updates)
self._from_db_object(self._context, self, rc)
break
except db_exc.DBDuplicateEntry as e:
# NOTE: e.columns 为空，所以直接出发后续的异常
if 'id' in e.columns:
# Race condition for ID creation; try again
continue
# The duplication is on the other unique column, 'name'. So do
# not retry; raise the exception immediately.
raise exception.ResourceClassExists(resource_class=self.name)
else:
# We have no idea how common it will be in practice for the retry
# limit to be exceeded. We set it high in the hope that we never
# hit this point, but added this log message so we know that this
# specific situation occurred.
LOG.warning("Exceeded retry limit on ID generation while "
"creating ResourceClass %(name)s",
{'name': self.name})
msg = _("creating resource class %s") % self.name
raise exception.MaxDBRetriesExceeded(action=msg)
继续看 db_exc.DBDuplicateEntry 的实现：
# /usr/lib/python2.7/site-packages/oslo_db/exception.py
class DBDuplicateEntry(DBError):
"""Duplicate entry at unique column error.
Raised when made an attempt to write to a unique column the same entry as
existing one. :attr: `columns` available on an instance of the exception
and could be used at error handling::
try:
instance_type_ref.save()
except DBDuplicateEntry as e:
if 'colname' in e.columns:
# Handle error.
:kwarg columns: a list of unique columns have been attempted to write a
duplicate entry.
:type columns: list
:kwarg value: a value which has been attempted to write. The value will
be None, if we can't extract it for a particular database backend. Only
MySQL and PostgreSQL 9.x are supported right now.
"""
def __init__(self, columns=None, inner_exception=None, value=None):
# 正常情况下，触发 DBDuplicateEntry 会将冲突的 columns 返回，让开发者得以方便的作出进一步判断
self.columns = columns or []
self.value = value
super(DBDuplicateEntry, self).__init__(inner_exception)
定位到生成冲突 columns 的地方：
# /opt/stack/queens/nova/.tox/functional/lib/python2.7/site-packages/oslo_db/sqlalchemy/exc_filters.py
@filters("sqlite", sqla_exc.IntegrityError,
(r"^.*columns?(?P<columns>[^)]+)(is|are)\s+not\s+unique$",
r"^.*UNIQUE\s+constraint\s+failed:\s+(?P<columns>.+)$",
r"^.*PRIMARY\s+KEY\s+must\s+be\s+unique.*$"))
def _sqlite_dupe_key_error(integrity_error, match, engine_name, is_disconnect):
"""Filter for SQLite duplicate key error.
note(boris-42): In current versions of DB backends unique constraint
violation messages follow the structure:
sqlite:
1 column - (IntegrityError) column c1 is not unique
N columns - (IntegrityError) column c1, c2, ..., N are not unique
sqlite since 3.7.16:
1 column - (IntegrityError) UNIQUE constraint failed: tbl.k1
N columns - (IntegrityError) UNIQUE constraint failed: tbl.k1, tbl.k2
sqlite since 3.8.2:
(IntegrityError) PRIMARY KEY must be unique
"""
columns = []
# NOTE(ochuprykov): We can get here by last filter in which there are no
# groups. Trying to access the substring that matched by
# the group will lead to IndexError. In this case just
# pass empty list to exception.DBDuplicateEntry
try:
columns = match.group('columns')
columns = [c.split('.')[-1] for c in columns.strip().split(", ")]
except IndexError:
pass
raise exception.DBDuplicateEntry(columns, integrity_error)
没有生产冲突 columns 的原因是：「底层 db engine 返回的 string match 不符合上述的匹配规范」。e.g.
2013-05-20 错误：('(sqlite3.IntegrityError) PRIMARY KEY must be unique',)
2019-04-16 正确：('(sqlite3.IntegrityError) UNIQUE constraint failed: resource_classes.id',)这是一个 SQLite3 版本不匹配导致的问题，但在 Nova 项目中却没有明确的指定 SQLite3 的版本，所以只能手动的修复这一问题。
解决
手动编译升级 SQLite3 的版本：
wget https://www.sqlite.org/2019/sqlite-autoconf-3280000.tar.gz
tar -xvf sqlite-autoconf-3280000.tar.gz
cd sqlite-autoconf-3280000
mkdir /opt/sqlite3
./configure --prefix=/opt/sqlite3
make && make install
升级完 SQLite3 依旧没有直接解决上述问题，这里主要涉及到一个 Python 如何调用 C so 库的问题，这也是解决这个问题的精髓所在。
- 首先我们找到 SQLite3 Python 客户端（API）的位置
$ python -c "import sqlite3; print(sqlite3.__file__)"
/usr/lib64/python2.7/sqlite3/__init__.pyc
- 查看 SQLite3 API 实现并找到 so 库导入语句
# /usr/lib64/python2.7/sqlite3/dbapi2.py
from _sqlite3 import *
- 查找 _sqlite3 so 库的位置
$ python -c 'import _sqlite3; print(_sqlite3)'
<module '_sqlite3' from '/opt/stack/queens/nova/.tox/functional/lib64/python2.7/lib-dynload/_sqlite3.so'>
- 查看 _sqlite3 so 库内含的动态函数库
$ ldd /opt/stack/queens/nova/.tox/functional/lib64/python2.7/lib-dynload/_sqlite3.so
linux-vdso.so.1 => (0x00007ffc4defb000)
libsqlite3.so.0 => /lib64/libsqlite3.so.0 (0x00007f708ba42000)
libpython2.7.so.1.0 => /lib64/libpython2.7.so.1.0 (0x00007f708b676000)
libpthread.so.0 => /lib64/libpthread.so.0 (0x00007f708b45a000)
libc.so.6 => /lib64/libc.so.6 (0x00007f708b08d000)
libz.so.1 => /lib64/libz.so.1 (0x00007f708ae77000)
libm.so.6 => /lib64/libm.so.6 (0x00007f708ab75000)
libdl.so.2 => /lib64/libdl.so.2 (0x00007f708a971000)
libutil.so.1 => /lib64/libutil.so.1 (0x00007f708a76e000)
/lib64/ld-linux-x86-64.so.2 (0x00007f708bf62000)
- 凭直觉，我们首先关注 libsqlite3.so.0 函数库
$ ls -alh /lib64/libsqlite3.so.0
lrwxrwxrwx. 1 root root 19 May 14 05:13 /lib64/libsqlite3.so.0 -> libsqlite3.so.0.8.6
$ ls -alh /lib64/libsqlite3.so.0.8.6
-rwxr-xr-x. 1 root root 5.1M Jun 4 05:51 /lib64/libsqlite3.so.0.8.6
至此，我们可以想到之所以升级了 SQLite3 的版本但依旧没有解决问题的原因是「Python 程序中调用的动态函数库依旧没有被更新」。所以我们只需要使用新安装的 so 文件替换掉就的就可以解决了。
mv /usr/lib64/libsqlite3.so.0.8.6 /usr/lib64/libsqlite3.so.0.8.6.bk
cp /opt/sqlite3/lib/libsqlite3.so.0.8.6 /usr/lib64/libsqlite3.so.0.8.6
最后
最后贴上 SQLite3 的修改 commit：
This issue is involved this commit, and introduced by version-3.8.2
...
commit eb743f01b125bebd8736ceb2873b69f27721b0ae
Author: D. Richard Hipp <drh@hwaci.com>
Date: Tue Nov 5 13:33:55 2013 +0000
Standardize the error messages generated by constraint failures to a format
of "$TYPE constraint failed: $DETAIL". This involves many changes to the
expected output of test cases.
...
解决这一问题主要的收获是 Python 程序和 C 程序之间的调用关键，如果两者之间并非是通过 TCP 协议来通信，而是通过 so 库文件来调用的话，那么我们需要注意 C 程序在 Linux 操作系统上的文件安装方式。并非单纯的升级了 C 程序就会立马在 Python 程序上生效，还要注意两者之间的桥梁（调用库文件）是否也一同升级了。
