openstack/deb-python-taskflow
Code Issues Proposed changes

Add in default transaction isolation levels

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Apply a default setting for transaction isolation levels
for mysql and postgresql to help avoid consistency issues
that happen when two transactions occur at the same time
on the same set of records.

Closes-Bug: 1326507

Change-Id: I1819722889d0d66d938641af6aa6f79fcfd2deb4
This commit is contained in:
Joshua Harlow
2014-06-04 12:49:54 -07:00
parent c8a281aa36
commit 848aaddb1a
1 changed files with 29 additions and 5 deletions
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34
taskflow/persistence/backends/impl_sqlalchemy.py
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@@ -95,6 +95,17 @@ POSTGRES_GONE_WAY_AWAY_ERRORS = (
# These connection urls mean sqlite is being used as an in-memory DB. # These connection urls mean sqlite is being used as an in-memory DB.
SQLITE_IN_MEMORY = ('sqlite://', 'sqlite:///', 'sqlite:///:memory:') SQLITE_IN_MEMORY = ('sqlite://', 'sqlite:///', 'sqlite:///:memory:')
# Transacation isolation levels that will be automatically applied, we prefer
# strong read committed isolation levels to avoid merging and using dirty
# data...
#
# See: http://en.wikipedia.org/wiki/Isolation_(database_systems)
DEFAULT_TXN_ISOLATION_LEVELS = {
'mysql': 'READ COMMITTED',
'postgresql': 'READ COMMITTED',
'postgres': 'READ COMMITTED',
}
def _in_any(reason, err_haystack): def _in_any(reason, err_haystack):
"""Checks if any elements of the haystack are in the given reason.""" """Checks if any elements of the haystack are in the given reason."""
@@ -189,6 +200,24 @@ class SQLAlchemyBackend(base.Backend):
('pool_timeout', 'pool_timeout')]: ('pool_timeout', 'pool_timeout')]:
if lookup_key in conf: if lookup_key in conf:
engine_args[k] = misc.as_int(conf.pop(lookup_key)) engine_args[k] = misc.as_int(conf.pop(lookup_key))
if 'isolation_level' not in conf:
# Check driver name exact matches first, then try driver name
# partial matches...
txn_isolation_levels = conf.pop('isolation_levels',
DEFAULT_TXN_ISOLATION_LEVELS)
level_applied = False
for (driver, level) in six.iteritems(txn_isolation_levels):
if driver == e_url.drivername:
engine_args['isolation_level'] = level
level_applied = True
break
if not level_applied:
for (driver, level) in six.iteritems(txn_isolation_levels):
if e_url.drivername.find(driver) != -1:
engine_args['isolation_level'] = level
break
else:
engine_args['isolation_level'] = conf.pop('isolation_level')
# If the configuration dict specifies any additional engine args # If the configuration dict specifies any additional engine args
# or engine arg overrides make sure we merge them in. # or engine arg overrides make sure we merge them in.
engine_args.update(conf.pop('engine_args', {})) engine_args.update(conf.pop('engine_args', {}))
@@ -384,11 +413,6 @@ class Connection(base.Connection):
def _save_logbook(self, session, lb): def _save_logbook(self, session, lb):
try: try:
lb_m = _logbook_get_model(lb.uuid, session=session) lb_m = _logbook_get_model(lb.uuid, session=session)
# NOTE(harlowja): Merge them (note that this doesn't provide
# 100% correct update semantics due to how databases have
# MVCC). This is where a stored procedure or a better backing
# store would handle this better by allowing this merge logic
# to exist in the database itself.
lb_m = _logbook_merge(lb_m, lb) lb_m = _logbook_merge(lb_m, lb)
except exc.NotFound: except exc.NotFound:
lb_m = _convert_lb_to_internal(lb) lb_m = _convert_lb_to_internal(lb)