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ZEO - Single-server client-server database server for ZODB

Project description

ZEO is a client-server storage for ZODB for sharing a single storage among many clients. When you use ZEO, a lower-level storage, typically a file storage, is opened in the ZEO server process. Client programs connect to this process using a ZEO ClientStorage. ZEO provides a consistent view of the database to all clients. The ZEO client and server communicate using a custom protocol layered on top of TCP.

Some alternatives to ZEO:

  • NEO is a distributed-server client-server storage.
  • RelStorage leverages the RDBMS servers to provide a client-server storage.

The documentation is available on readthedocs.

Changelog

5.2.3 (2021-08-09)

  • Ensure ZEO satisfies the ZODB >= 5.6 requirement that lastTransaction() changes only after invalidation processing. Violating this requirement can lead to race conditions and associated data corruption #166.
  • Add automated tests against the ZODB master branch see issue 177.
  • Fix data corruption due to race between load and external invalidations. See issue 155.
  • Improve log message when client cache is out of sync with server. See issue 142.

5.2.2 (2020-08-11)

  • Remove support for Python 3.4
  • Provide proper CA test certificates to allow the SSL tests succeed for Py3
  • Replace deprecated occurrences of Thread.isAlive() by Thread.is_alive() See pull request 154.
  • Include both modified and just created objects into invalidations. See pull request 160.

5.2.1 (2019-02-09)

  • Add support for Python 3.7.
  • Switch from msgpack-python to msgpack. Currently a version < 0.6 is required.
  • Stop calling the deprecated checkSecure method when creating a ClientStorage. With ZODB 5.2.2 and above, this issued a warning. With older versions, this could issue a log message, but this was considered a misfeature. See issue 134.

5.2.0 (2018-03-28)

  • Fixed: The quickstart/ad-hoc/play ZEO server relied on test dependencies. See issue 105.

  • Disallow passing strings as addresses to ClientStorage under Windows because string addresses are used for unix-domain sockets, which aren’t supported on Windows. See issue 107.

  • Renamed all async attributes to async_ for compatibility with Python 3.7. See issue 104.

  • Fixed to work with some changes made in ZODB 5.4.0.

    Client-side updates are incuded for ZODB 5.4.0 or databases that already had zodbpickle.binary OIDs. See issue 113.

  • ZEO now uses pickle protocol 3 for both Python 2 and Python 3. (Previously protocol 1 was used for Python 2.) This matches the change in ZODB 5.4.0.

5.1.2 (2018-03-27)

  • Fix: ZEO didn’t work with a change in ZODB 5.4.0.

    (Allow zodbpickle.binary to be used in RPC requests, which is necessary for compatibility with ZODB 5.4.0 on Python 2. See issue 107.)

5.1.1 (2017-12-18)

  • All classes are new-style classes on Python 2 (they were already new-style on Python 3). This improves performance on PyPy. See issue 86.
  • Fixed removing UNIX socket files under Python 2 with ZConfig 3.2.0. See issue 90.

5.1.0 (2017-04-03)

  • Added support for serializing ZEO messages using msgpack rather than pickle. This helps pave the way to supporting byteserver, but it also allows ZEO servers to support Python 2 or 3 clients (but not both at the same time) and may provide a small performance improvement.
  • Possibly fixed the deprecated and untested zeoctl script.
  • Removed zeopasswd, which no longer makes sense given that ZEO authentication was removed, in favor of SSL.

5.0.4 (2016-11-18)

  • Fixed: ZEO needed changes to work with recent transaction changes.

    ZEO now works with the latest versions of ZODB and transaction

5.0.3 (2016-11-18)

  • Temporarily require non-quite-current versions of ZODB and transaction until we can sort out some recent breakage.

5.0.2 (2016-11-02)

  • Provide much better performance on Python 2.
  • Provide better error messages when pip tries to install ZEO on an unsupported Python version. See issue 75.

5.0.1 (2016-09-06)

Packaging-related doc fix

5.0.0 (2016-09-06)

This is a major ZEO revision, which replaces the ZEO network protocol implementation.

New features:

  • SSL support

  • Optional client-side conflict resolution.

  • Lots of mostly internal clean ups.

  • ClientStorage``server-sync configuration option and server_sync constructor argument to force a server round trip at the beginning of transactions to wait for any outstanding invalidations at the start of the transaction to be delivered.

  • Client disconnect errors are now transient errors. When applications retry jobs that raise transient errors, jobs (e.g. web requests) with disconnect errors will be retried. Together with blocking synchronous ZEO server calls for a limited time while disconnected, this change should allow brief disconnections due to server restart to avoid generating client-visible errors (e.g. 500 web responses).

  • ClientStorage prefetch method to prefetch oids.

    When oids are prefetched, requests are made at once, but the caller doesn’t block waiting for the results. Rather, then the caller later tries to fetch data for one of the object ids, it’s either delivered right away from the ZEO cache, if the prefetch for the object id has completed, or the caller blocks until the inflight prefetch completes. (No new request is made.)

Dropped features:

  • The ZEO authentication protocol.

    This will be replaced by new authentication mechanims leveraging SSL.

  • The ZEO monitor server.

  • Full cache verification.

  • Client suppprt for servers older than ZODB 3.9

  • Server support for clients older than ZEO 4.2.0

5.0.0b0 (2016-08-18)

  • Added a ClientStorage server-sync configuration option and server_sync constructor argument to force a server round trip at the beginning of transactions to wait for any outstanding invalidations at the start of the transaction to be delivered.
  • When creating an ad hoc server, a log file isn’t created by default. You must pass a log option specifying a log file name.
  • The ZEO server register method now returns the storage last transaction, allowing the client to avoid an extra round trip during cache verification.
  • Client disconnect errors are now transient errors. When applications retry jobs that raise transient errors, jobs (e.g. web requests) with disconnect errors will be retried. Together with blocking synchronous ZEO server calls for a limited time while disconnected, this change should allow brief disconnections due to server restart to avoid generating client-visible errors (e.g. 500 web responses).
  • Fixed bugs in using the ZEO 5 client with ZEO 4 servers.

5.0.0a2 (2016-07-30)

  • Added the ability to pass credentials when creating client storages.

    This is experimental in that passing credentials will cause connections to an ordinary ZEO server to fail, but it facilitates experimentation with custom ZEO servers. Doing this with custom ZEO clients would have been awkward due to the many levels of composition involved.

    In the future, we expect to support server security plugins that consume credentials for authentication (typically over SSL).

    Note that credentials are opaque to ZEO. They can be any object with a true value. The client mearly passes them to the server, which will someday pass them to a plugin.

5.0.0a1 (2016-07-21)

  • Added a ClientStorage prefetch method to prefetch oids.

    When oids are prefetched, requests are made at once, but the caller doesn’t block waiting for the results. Rather, then the caller later tries to fetch data for one of the object ids, it’s either delivered right away from the ZEO cache, if the prefetch for the object id has completed, or the caller blocks until the inflight prefetch completes. (No new request is made.)

  • Fixed: SSL clients of servers with signed certs didn’t load default certs and were unable to connect.

5.0.0a0 (2016-07-08)

This is a major ZEO revision, which replaces the ZEO network protocol implementation.

New features:

  • SSL support
  • Optional client-side conflict resolution.
  • Lots of mostly internal clean ups.

Dropped features:

  • The ZEO authentication protocol.

    This will be replaced by new authentication mechanims leveraging SSL.

  • The ZEO monitor server.

  • Full cache verification.

  • Client suppprt for servers older than ZODB 3.9

  • Server support for clients older than ZEO 4.2.0

4.2.0 (2016-06-15)

  • Changed loadBefore to operate more like load behaved, especially with regard to the load lock. This allowes ZEO to work with the upcoming ZODB 5, which used loadbefore rather than load.

    Reimplemented load using loadBefore, thus testing loadBefore extensively via existing tests.

  • Other changes to work with ZODB 5 (as well as ZODB 4)

  • Fixed: the ZEO cache loadBefore method failed to utilize current data.

  • Drop support for Python 2.6 and 3.2.

  • Fix AttributeError: ‘ZEOServer’ object has no attribute ‘server’ when StorageServer creation fails.

4.2.0b1 (2015-06-05)

  • Add support for PyPy.

4.1.0 (2015-01-06)

  • Add support for Python 3.4.
  • Added a new ruok client protocol for getting server status on the ZEO port without creating a full-blown client connection and without logging in the server log.
  • Log errors on server side even if using multi threaded delay.

4.0.0 (2013-08-18)

  • Avoid reading excess random bytes when setting up an auth_digest session.
  • Optimize socket address enumeration in ZEO client (avoid non-TCP types).
  • Improve Travis CI testing support.
  • Assign names to all threads for better runtime debugging.
  • Fix “assignment to keyword” error under Py3k in ‘ZEO.scripts.zeoqueue’.

4.0.0b1 (2013-05-20)

  • Depend on ZODB >= 4.0.0b2
  • Add support for Python 3.2 / 3.3.

4.0.0a1 (2012-11-19)

First (in a long time) separate ZEO release.

Since ZODB 3.10.5:

  • Storage servers now emit Serving and Closed events so subscribers can discover addresses when dynamic port assignment (bind to port 0) is used. This could, for example, be used to update address information in a ZooKeeper database.
  • Client storages have a method, new_addr, that can be used to change the server address(es). This can be used, for example, to update a dynamically determined server address from information in a ZooKeeper database.

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