CHANGES.txt

Zope Enterprise Option (ZEO) Revision History

  ZEO 0.2 

    This release is expected to be close to beta quality. Initially, the
    primary goals of this release were to:

      - Correct some consistency problems that had been observed in
        0.1 on starup.

      - Allow ZEO clients to detect, survive, and recover from
        disconnection from the ZEO server.

    Based on some feedback from some folks who tried 0.1, improving
    write performance was made a priority.

    Features

      - The ZEO Client now handles server failures gracefully:

        o The client with a persistent cache can generally startup
	  even if the server is not running, assuming that it has at
	  least a minimal number of objects in the cache.

        o The client will continue to function even if the server
          connection is interuppted.

        o Server availability is detected by the client (which tries
          to connect to the server every few minutes). A disconnected
          client will automatically reconnect to an available server.

        o When the client is disconnected, write transactions cannot
          be performed.  Reads fail for objects that are not in the
          cache.

      - Performance enhancements

        The speed of write-intensive operations have been improved
	approximately 70%.  When using Unix domain sockets for
	client/server communication, ZEO transactions take roughly 2-3
	times as long as FileStorage transactions to commit.
	(This was based on some tests. Your mileage may vary.)

      - Packing support was added. Note that packing is done
        asynchrounously. The client returns immediately from a pack
        call. The server packs in a thread and sends updated
        statistics to the client when packing is completed.

      - Support for Unix-domain sockets was added.

      - Pickles sent to the server are now checked to make sure that
        they don't contain unapproved instance or global-variable
        (function) pickles.

    Bugs fixed

      - Data could be badly inconsistent when a persistent cache
        was started, due to a bug in the cache initialization logic.
      
      - The application was allowed to begin operation while the cache
        was being verified. This could lead to harmful inconsistencies.

    Changes made to Zope to support ZEO

      - A number of changes were made to ZODB to support asynchronous
        storage during transaction commit.

      - Normally Zope updates the database during startup to reflect
        product changes. This behavior is now suppressed when the
        ZEO_CLIENT environment variable is set. It doesn't make sense
        for many clients to update the database for the same products.

      - The asyncore module was modified to add support for multiple
        asyncore loops. This change was applied to asyncore in the
        Zope and the (official, owned by Sam Rushing) medusa CVS
        trees.

      - A new module, ThreadedAsync.py has been added in the Zope
        lib/python directory.  This module provides notification to
        async objects (like ZEO clients) to let them know when the
        asyncore main loop has started. This was needed to enable use
        of async code before the main loop starts.

  ZEO 0.1 (aka "iteration 1")

    This was an initial alpha of ZEO that demonstrated basic
    functionalities. It lacked robustness and has some performance
    problems on writes.