场景：
Greenplum在Mac上源码编译安装的时候，首先需要安装ORCA，安装ORCA的过程中，报错了。
报错内容：
ChrisdeMacBook-Pro:depends chris$ make
CONAN_USER_HOME=/Users/chris/git/gpdb/depends conan install --build=missing conanfile_orca.txt
orca/v2.56.0@gpdb/stable: Not found in local cache, looking in remotes...
orca/v2.56.0@gpdb/stable: Trying with 'conan-center'...
From cffi callback :
Traceback (most recent call last):
File "/usr/local/lib/python2.7/site-packages/OpenSSL/SSL.py", line 313, in wrapper
_lib.X509_up_ref(x509)
AttributeError: 'module' object has no attribute 'X509_up_ref'
ERROR: HTTPSConnectionPool(host='', port=443): Max retries exceeded with url: /v1/conans/orca/v2.56.0/gpdb/stable/download_urls (Caused by SSLError(SSLError("bad handshake: Error([('SSL routines', 'tls_process_server_certificate', 'certificate verify failed')],)",),))
Unable to connect to conan-center=
https://
make: *** [orca] Error 1
报错原因：
复查前面的步骤，发现有一步python库冲突：
pyopenssl 17.5.0 has requirement cryptography>=2.1.4, but you'll have cryptography 1.9 which is incompatible.
解决方法：
卸载冲突库后重新make编译即可。
ChrisdeMacBook-Pro:depends chris$ pip2 uninstall cryptography
Uninstalling cryptography-1.9:
Would remove:
/usr/local/lib/python2.7/site-packages/cryptography-1.9.dist-info/*
/usr/local/lib/python2.7/site-packages/cryptography/*
Proceed (y/n)? y
Successfully uninstalled cryptography-1.9
