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Creating ZODB¶

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PyAMS primarily relies on a ZODB (Zope Objects DataBase) to store it’s configuration. Other packages may -rely on other database(s), but PyAMS_content package also stores it’s contents in a ZODB.

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As some PyAMS packages start several processes (“synchronization” is done via ØMQ), concurrent accesses are -required on the ZODB (even when you start your application in “single process” mode); several ZODB storages -implementations providing a shared access are available: ZEO, RelStorage and Newt.DB.

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Installing a ZEO server¶

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ZEO (Zope Enterprise Objects) is the first available implementation available for concurrent access to a -FileStorage, provided through the ZEO package.

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ZEO package documentation and complete configuration settings are available on PyPI.

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Creating initial buildout¶

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PyAMS provides a ZEO server scaffold, called zeo_server, generated via a cookiecutter template.

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A simple option to create a ZEO server is to create a buildout environment including ZEO and ZODB packages:

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# mkdir /var/local/
-# pip3 install virtualenv
-# virtualenv --python=python3.5 env
-# cd env
-# . bin/activate
-(env) # pip3.5 install cookiecutter
-(env) # cookiecutter hg+http://hg.ztfy.org/pyams/scaffolds/zeo_server
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CookieCutter will ask you for a small set of input variables that you can change or not:

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pyams_release: version of PyAMS configuration file to use. “latest” (default value) will point to last release; -you can also choose to point to a given release (“0.1.4” for example)
project_name: current environment name in “human form”
project_slug: “technical” package name, based on project name
eggs_directory: relative or absolute path to directory containing downloaded eggs; this directory can be -shared with other projects (“eggs” as default)
run_user: user name under which ZEO process will run (“zeoadm” as default)
run_group: group name under which ZEO process will run (“zeo” as default)
zeo_server_port: listening port of ZEO server (“8100” as default)
zeo_monitor_port: listening port of ZEO monitor (“8101” as default)
zeo_storage: name of first ZEO storage; default value is based on project name
use_zeo_auth: specify if ZEO authentication should be used
zeo_auth_user: name of ZEO authenticated user (if ZEO authentication is used)
zeo_auth_password: password of ZEO authenticated user (if ZEO authentication is used)
zeo_pack_report: email address to which pack reports should be sent
logs_directory: absolute path to directory containing ZEO’s log files.

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A message is displayed after initialization to finalize environment creation:

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Your ZEO environment is initialized.
-To finalize it''s creation, just type:
-- cd zeo_server
-- python3.5 bootstrap.py
-- ./bin/buildout
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-To initialize authentication database, please run following command after buildout:
-./bin/zeopasswd -f etc/auth.db -p digest -r "ZEO_server" zeouser xxxx
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ZEO server configuration¶

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All ZEO configuration files are generated in “etc” subdirectory. These includes:

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etc/zeo_server-zdaemon.conf: ZDaemon configuration file
etc/zeo_server-zeo.conf: ZEO server configuration file
etc/auth.db: ZEO authentication file; WARNING: this file is not created automatically, you have to create it -after buildout.

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In these file names, always replace “zeo_server” with the value which was given to “project_slug” variable during -CookieCutter template creation.

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ZEO server tools¶

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A set of system configuration files are produced to handle your ZEO environment. These includes:

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etc/init.d/zeo-zeo_server: ZEO server start/stop script in Init-D format. Create a link to this file in -/etc/init.d and update Init.d scripts (update-rc.d zeo-zeo_server defaults) to include ZEO in server start/stop -process. You can also use this script to start/stop ZEO by hand with start and stop arguments.
etc/systemd/zeo-zeo_server.service: SystemD service configuration file for ZEO server. Create a link to this -file in /etc/systemd/system and reload SystemD daemon (systemctl daemon-reload) before activating ZEO service -(systemctl enable zeo-zeo_server.service and systemctl start zeo-zeo_server.service).
etc/logrotate.d/zeo-zeo_server: LogRotate configuration file for ZEO log files. Create a link to this file in -/etc/logrotate.d to activate log rotation for ZEO server.
etc/cron.d/pack-zeo-zeo_server: Cron configuration file for ZEO database packing. Just create a link to this -file in /etc/cron.d directory to enable ZODB packing on a weekly basis (by default).

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In these file names, always replace “zeo_server” with the value which was given to “project_slug” variable during -CookieCutter template creation. All directory names are those used on a Debian GNU/Linux distribution and may have -to be changed on other distributions.

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Installing a RelStorage server¶

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RelStorage (http://relstorage.readthedocs.io/en/latest) is an alternate ZODB storage implementation, that stores -Python pickles in a relational database; PostgreSQL (>= 9.0), MySQL (>= 5.0.32) and Oracle (> 10g) databases are -supported.

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To create a database compatible with RelStorage, you just have to install the database server and create a database -dedicated to RelStorage; schema initialization is then completely done by RelStorage on application startup.

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RelStorage is supposed to provide better performances than ZEO, notably under high load. RelStorage can also get -benefit from many extensions (clustering, fail-over, hot-standby…) provided by these databases.

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Installing a NewtDB server¶

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NewtDB (http://www.newtdb.org/en/latest) is another ZODB storage implementation. It’s using RelStorage but is -dedicated to PostgreSQL (>= 9.5).

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NewtDB adds conversion of data from the native serialization used by ZODB to JSON, stored in a PostgreSQL JSONB -column. The JSON data supplements the native data to support indexing, search, and access from non-Python application. -Because the JSON format is lossy, compared to the native format, the native format is still used for loading -objects from the database. For this reason, the JSON data are read-only.

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Newt adds a search API for searching the Postgres JSON data and returning persistent objects. It also provides a -convenient API for raw data searches.

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Database creation is done as with RelStorage, but NewtDB add several schema objects. Migration scripts are available -if you need to switch from a classic RelStorage database to a Newt database.

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