Commit b6716261 authored by Tim Peters's avatar Tim Peters

Forward port from Zope 2.7 branch.

Repaired a bug wherein spurious error msgs could be produced after
reporting a problem with an unloadable object (discovered by eyeball,
while staring at the code to figure out what it actually does).

Vastly expanded the module docstring, with a slimmed-down version of
the new fsrefs docs on the ZODB Wiki.
parent df23d95f
......@@ -32,6 +32,13 @@ warning level; if time appears to have run backwards at least 30
minutes, the message is logged at critical level (and you should
investigate to find and repair the true cause).
Tools
-----
fsrefs.py: Fleshed out the module docstring, and repaired a bug
wherein spurious error msgs could be produced after reporting a
problem with an unloadable object.
Test suite
----------
......
......@@ -16,10 +16,51 @@
"""Check FileStorage for dangling references.
usage: fsrefs.py data.fs
usage: fsrefs.py [-v] data.fs
This script ignores versions, which might produce incorrect results
for storages that use versions.
fsrefs.py checks object sanity by trying to load the current revision of
every object O in the database, and also verifies that every object
directly reachable from each such O exists in the database. Note that
application code implementing objects (or at least defining their classes)
must be available, an d on PYTHONPATH, for fsrefs to work, because objects
are actually loaded. On a ZEO server, all the application code typically
isn't present, so it may be difficult to run fsrefs usefully on a ZEO
server.
A read-only connection to the specified FileStorage is made, but it is not
recommended to run fsrefs against a live FileStorage. Because a live
FileStorage is mutating while fsrefs runs, it's not possible for fsrefs to
get a wholly consistent view of the database across the entire time fsrefs
is running; spurious error messages may result.
fsrefs doesn't normally produce any output. If an object fails to load, the
oid of the object is given in a message saying so, and if -v was specified
then the traceback corresponding to the load failure is also displayed
(this is the only effect of the -v flag, and is usually very helpful; -v is
recommended for normal use). Note that, as mentioned above, a common
problem is to get a "failed to load" message simply because the module
containing the class of the object isn't on PYTHONPATH.
Two other kinds of errors are also detected, one strongly related to
"failed to load", when an object O loads OK, and directly refers to a
persistent object P but there's a problem with P:
- If P doesn't exist in the database, a message saying so is displayed.
The unsatisifiable reference to P is often called a "dangling
reference"; P is called "missing" in the error output.
- If it was earlier determined that P could not be loaded (but does exist
in the database), a message saying that O refers to an object that can't
be loaded is displayed. Note that fsrefs only makes one pass over the
database, so if an object O refers to an unloadable object P, and O is
seen by fsrefs before P, an "O refers to the unloadable P" message will
not be produced; a message saying that P can't be loaded will be
produced when fsrefs later tries to load P, though.
Note these limitations: because fsrefs only looks at the current revision
of objects, it does not attempt to load objects in versions, or non-current
revisions of objects; therefore fsrefs cannot find problems in versions or
in non-current revisions.
"""
from ZODB.FileStorage import FileStorage
......@@ -73,10 +114,12 @@ def main(path):
traceback.print_exc()
noload[oid] = 1
# XXX If we get here after we've already loaded objects
# that refer to this one, we won't get error reports from
# them. We could fix this by making two passes over the
# storage, but that seems like overkill.
# If we get here after we've already loaded objects
# that refer to this one, we will not have gotten error reports
# from the latter about the current object being unloadable.
# We could fix this by making two passes over the storage, but
# that seems like overkill.
continue
refs = get_refs(data)
missing = [] # contains 3-tuples of oid, klass-metadata, reason
......
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