Package: zc.zlibstorage
ZODB storage wrapper for zlib compression of database recordsThezc.zlibstoragepackage provides ZODB storage wrapper
implementations that provides compression of database records.ContentsZODB storage wrapper for zlib compression of database recordsUsageUse with ZEODecompressing onlyCompressing entire databasesRecord prefixStand-alone Compression and decompression functionsChanges1.2.0 (2017-01-20)1.1.0 (2016-08-03)1.0.0 (2015-11-11)0.1.1 (2010-05-26)0.1.0 (2010-05-20)UsageThe primary storage iszc.zlibstorage.ZlibStorage.  It is used as
a wrapper around a lower-level storage.  From Python, it is
constructed by passing another storage, as in:import ZODB.FileStorage, zc.zlibstorage

storage = zc.zlibstorage.ZlibStorage(
    ZODB.FileStorage.FileStorage('data.fs'))When using a ZODB configuration file, the zlibstorage tag is used:%import zc.zlibstorage

<zodb>
  <zlibstorage>
    <filestorage>
      path data.fs
    </filestorage>
  </zlibstorage>
</zodb>Note the%importused to load the definition of thezlibstoragetag.Use with ZEOWhen used with a ZEO ClientStorage, you’ll need to use a server zlib
storage on the storage server.  This is necessary so that server
operations that need to get at uncompressed record data can do so.
This is accomplished using theserverzlibstoragetag in your ZEO
server configuration file:%import zc.zlibstorage

<zeo>
  address 8100
</zeo>

<serverzlibstorage>
  <filestorage>
    path data.fs
  </filestorage>
</serverzlibstorage>Applying compression on the client this way is attractive because, in
addition to reducing the size of stored database records on the
server, you also reduce the size of records sent from the server to the
client and the size of records stored in the client’s ZEO cache.Decompressing onlyBy default, records are compressed when written to the storage and
uncompressed when read from the storage.  Acompressoption can be
used to disable compression of records but still uncompress compressed
records if they are encountered. Here’s an example from in Python:import ZODB.FileStorage, zc.zlibstorage

storage = zc.zlibstorage.ZlibStorage(
    ZODB.FileStorage.FileStorage('data.fs'),
    compress=False)and using the configurationb syntax:%import zc.zlibstorage

<zodb>
  <zlibstorage>
    compress false
    <filestorage>
      path data.fs
    </filestorage>
  </zlibstorage>
</zodb>This option is useful when deploying the storage when there are
multiple clients.  If you don’t want to update all of the clients at
once, you can gradually update all of the clients with a zlib storage
that doesn’t do compression, but recognizes compressed records.  Then,
in a second phase, you can update the clients to compress records, at
which point, all of the clients will be able to read the compressed
records produced.Compressing entire databasesOne way to compress all of the records in a database is to copy data
from an uncompressed database to a compressed one, as in:import ZODB.FileStorage, zc.zlibstorage

orig = ZODB.FileStorage.FileStorage('data.fs')
new = zc.zlibstorage.ZlibStorage(
    ZODB.FileStorage.FileStorage('data.fs-copy'))
new.copyTransactionsFrom(orig)

orig.close()
new.close()Record prefixCompressed records have a prefix of “.z”.  This allows a database to
have a mix of compressed and uncompressed records.Stand-alone Compression and decompression functionsIn anticipation of wanting to plug the compression and decompression
logic into other tools without creating storages, the functions used
to compress and uncompress data records are available aszc.zlibstoragemodule-level functions:compress(data)Compress the given data if:it is a string more than 20 characters in length,it doesn’t start with the compressed-record marker,b'.z', andthe compressed size is less the original.The compressed (or original) data are returned.decompress(data)Decompress the data if it is compressed.The decompressed (or original) data are returned.Changes1.2.0 (2017-01-20)Add support for Python 3.6 and PyPy.Test with both ZODB/ZEO 4 and ZODB/ZEO 5.
Note that ServerZlibStorage cannot be used in a ZODB 5 Connection
(e.g., client-side, which wouldn’t make sense :-]).
(https://github.com/zopefoundation/zc.zlibstorage/issues/5).Close the underlying iterator used by theiteratorwrapper when
it is closed. (https://github.com/zopefoundation/zc.zlibstorage/issues/4)1.1.0 (2016-08-03)Fixed an incompatibility with ZODB5.  The previously optional and
ignored version argument to the databaseinvalidatemethod is now
disallowed.Drop Python 2.6, 3.2, and 3.3 support. Added Python 3.4 and 3.5 support.1.0.0 (2015-11-11)Python 3 support contributed by Christian Tismer.0.1.1 (2010-05-26)Fixed a packaging bug.0.1.0 (2010-05-20)Initial release