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ovsdb: Force strong references to non-root tables to be persistent.

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When a strong reference to a non-root table is ephemeral, the database log
can contain inconsistencies.  In particular, if the column in question is
the only reference to a row, then the row will be created in one logged
transaction but the reference to it will not be logged (because it is
ephemeral).  Thus, any later occurrence of the row later in the log (to
modify it, to delete it, or just to reference it) will yield a transaction
error and reading the database will abort at that point.

This commit fixes the problem by forcing any column with a strong reference
to a non-root table to be persistent.

The change to ovsdb_schema_from_json() looks bigger than it really is: it
just swaps the order of two operations on the schema and updates their
comments.  Similarly for the update to ovs.db.DbSchema.__init__().

Bug #5144.
Reported-by: Sujatha Sumanth <ssumanth@nicira.com>
Bug #5149.
Reported-by: Ram Jothikumar <rjothikumar@nicira.com>
This commit is contained in:
Ben Pfaff
2011-03-31 16:43:43 -07:00
parent 219c9a73dc
commit 42a49b9601
4 changed files with 107 additions and 32 deletions
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35
python/ovs/db/schema.py
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@@ -27,13 +27,6 @@ class DbSchema(object):
self.version = version
self.tables = tables
# Validate that all ref_tables refer to the names of tables
# that exist.
for table in self.tables.itervalues():
for column in table.columns.itervalues():
self.__check_ref_table(column, column.type.key, "key")
self.__check_ref_table(column, column.type.value, "value")
# "isRoot" was not part of the original schema definition. Before it
# was added, there was no support for garbage collection. So, for
# backward compatibility, if the root set is empty then assume that
@@ -42,6 +35,17 @@ class DbSchema(object):
for table in self.tables.itervalues():
table.is_root = True
# Validate that all ref_tables refer to the names of tables
# that exist.
#
# Also force certain columns to be persistent, as explained in
# __check_ref_table(). This requires 'is_root' to be known, so this
# must follow the loop updating 'is_root' above.
for table in self.tables.itervalues():
for column in table.columns.itervalues():
self.__check_ref_table(column, column.type.key, "key")
self.__check_ref_table(column, column.type.value, "value")
def __root_set_size(self):
"""Returns the number of tables in the schema's root set."""
n_root = 0
@@ -91,12 +95,25 @@ class DbSchema(object):
return json
def __check_ref_table(self, column, base, base_name):
if (base and base.type == types.UuidType and base.ref_table and
base.ref_table not in self.tables):
if not base or base.type != types.UuidType or not base.ref_table:
return
ref_table = self.tables.get(base.ref_table)
if not ref_table:
raise error.Error("column %s %s refers to undefined table %s"
% (column.name, base_name, base.ref_table),
tag="syntax error")
if base.is_strong_ref() and not ref_table.is_root:
# We cannot allow a strong reference to a non-root table to be
# ephemeral: if it is the only reference to a row, then replaying
# the database log from disk will cause the referenced row to be
# deleted, even though it did exist in memory. If there are
# references to that row later in the log (to modify it, to delete
# it, or just to point to it), then this will yield a transaction
# error.
column.persistent = True
class IdlSchema(DbSchema):
def __init__(self, name, version, tables, idlPrefix, idlHeader):
DbSchema.__init__(self, name, version, tables)