diff options
| -rw-r--r-- | doc/build/changelog/unreleased_12/4071.rst | 13 | ||||
| -rw-r--r-- | doc/build/faq/performance.rst | 50 | ||||
| -rw-r--r-- | lib/sqlalchemy/orm/mapper.py | 15 | ||||
| -rw-r--r-- | lib/sqlalchemy/orm/strategies.py | 26 | ||||
| -rw-r--r-- | test/orm/test_mapper.py | 25 |
5 files changed, 16 insertions, 113 deletions
diff --git a/doc/build/changelog/unreleased_12/4071.rst b/doc/build/changelog/unreleased_12/4071.rst new file mode 100644 index 000000000..ff6fc1bb0 --- /dev/null +++ b/doc/build/changelog/unreleased_12/4071.rst @@ -0,0 +1,13 @@ +.. change:: + :tags: bug, orm + :tickets: 4071 + + Removed the warnings that are emitted when the LRU caches employed + by the mapper as well as loader srtategies reach their threshold; the + purpose of this warning was at first a guard against excess cache keys + being generated but became basically a check on the "creating many + engines" antipattern. While this is still an antipattern, the presense + of test suites which both create an engine per test as well as raise + on all warnings will be an inconvenience; it should not be critical + that such test suites change their architecture just for this warning + (though engine-per-test suite is always better).
\ No newline at end of file diff --git a/doc/build/faq/performance.rst b/doc/build/faq/performance.rst index c6f51ebb1..d6ee557ea 100644 --- a/doc/build/faq/performance.rst +++ b/doc/build/faq/performance.rst @@ -460,53 +460,3 @@ Script:: test_sqlite3(100000) -.. _faq_compiled_cache_threshold: - -How do I deal with "compiled statement cache reaching its size threshhold"? ---------------------------------------------------------------------------- - -Some parts of the ORM make use of a least-recently-used (LRU) cache in order -to cache generated SQL statements for fast reuse. More generally, these -areas are making use of the "compiled cache" feature of :class:`.Connection` -which can be invoked using :meth:`.Connection.execution_options`. - -The following two points summarize what should be done if this warning -is occurring: - -* Ensure the application **does not create an arbitrary number of - Engine objects**, that is, it does not call :func:`.create_engine` on - a per-operation basis. An application should have only **one Engine per - database URL**. - -* If the application does not have an unbounded number of engines, - **report the warning to the SQLAlchemy developers**. Guidelines on - mailing list support is at: http://www.sqlalchemy.org/support.html#mailinglist - -The cache works by creating a cache key that can uniquely identify the -combination of a specific dialect and a specific Core SQL expression. -A cache key that already exists in the cache will reuse the already-compiled -SQL expression. A cache key that doesn't exist will create a *new* entry -in the dictionary. When this dictionary reaches the configured threshhold, -the LRU cache will trim the size of the cache back down by a certain percentage. - -It is important to understand that from the above, **a compiled cache that -is reaching its size limit will perform badly.** This is because not only -are the SQL statements being freshly compiled into strings rather than using -the cached version, but the LRU cache is also spending lots of time trimming -its size back down. - -The primary reason the compiled caches can grow is due to the **antipattern of -using a new Engine for every operation**. Because the compiled cache -must key on the :class:`.Dialect` associated with an :class:`.Engine`, -calling :func:`.create_engine` many times in an application will establish -new cache entries for every engine. Because the cache is self-trimming, -the application won't grow in size unbounded, however the application should -be repaired to not rely on an unbounded number of :class:`.Engine` -objects. - -Outside of this pattern, the default size limits set for these caches within -the ORM should not generally require adjustment, and the LRU boundaries -should never be reached. If this warning is occurring and the application -is not generating hundreds of engines, please report the issue to the -SQLAlchemy developers on the mailing list; see the guidelines -at http://www.sqlalchemy.org/support.html#mailinglist. diff --git a/lib/sqlalchemy/orm/mapper.py b/lib/sqlalchemy/orm/mapper.py index 9b9457213..1d172f71a 100644 --- a/lib/sqlalchemy/orm/mapper.py +++ b/lib/sqlalchemy/orm/mapper.py @@ -2871,20 +2871,7 @@ class Mapper(InspectionAttr): @_memoized_configured_property def _compiled_cache(self): - return util.LRUCache(self._compiled_cache_size, - size_alert=self._alert_lru_cache_limit) - - def _alert_lru_cache_limit(self, lru_cache): - util.warn( - "Compiled statement cache for mapper %s is " - "reaching its size threshold of %d, based on _compiled_cache_size " - "of %d. Please refer to " - "http://docs.sqlalchemy.org/en/latest/faq/performance.html" - "#faq_compiled_cache_threshold" - " for best practices." % - (self, - lru_cache.size_threshold, - self._compiled_cache_size)) + return util.LRUCache(self._compiled_cache_size) @_memoized_configured_property def _sorted_tables(self): diff --git a/lib/sqlalchemy/orm/strategies.py b/lib/sqlalchemy/orm/strategies.py index 11ebcee50..a57b66045 100644 --- a/lib/sqlalchemy/orm/strategies.py +++ b/lib/sqlalchemy/orm/strategies.py @@ -643,18 +643,7 @@ class LazyLoader(AbstractRelationshipLoader, util.MemoizedSlots): @util.dependencies("sqlalchemy.ext.baked") def _memoized_attr__bakery(self, baked): - return baked.bakery(size=50, _size_alert=self._alert_lru_cache_limit) - - def _alert_lru_cache_limit(self, lru_cache): - util.warn( - "Compiled statement cache for lazy loader on attribute %s is " - "reaching its size threshold of %d. Consider setting " - "bake_queries=False for this relationship. Please refer to " - "http://docs.sqlalchemy.org/en/latest/faq/performance.html" - "#faq_compiled_cache_threshold" - " for best practices." % - (self.parent_property, - lru_cache.size_threshold)) + return baked.bakery(size=50) @util.dependencies( "sqlalchemy.orm.strategy_options") @@ -1851,18 +1840,7 @@ class SelectInLoader(AbstractRelationshipLoader, util.MemoizedSlots): @util.dependencies("sqlalchemy.ext.baked") def _memoized_attr__bakery(self, baked): - return baked.bakery(size=50, _size_alert=self._alert_lru_cache_limit) - - def _alert_lru_cache_limit(self, lru_cache): - util.warn( - "Compiled statement cache for selectin loader on attribute %s is " - "reaching its size threshold of %d. Consider setting " - "bake_queries=False for this relationship. Please refer to " - "http://docs.sqlalchemy.org/en/latest/faq/performance.html" - "#faq_compiled_cache_threshold" - " for best practices." % - (self.parent_property, - lru_cache.size_threshold)) + return baked.bakery(size=50) def create_row_processor( self, context, path, loadopt, mapper, diff --git a/test/orm/test_mapper.py b/test/orm/test_mapper.py index f39e174b0..42d114f6f 100644 --- a/test/orm/test_mapper.py +++ b/test/orm/test_mapper.py @@ -262,31 +262,6 @@ class MapperTest(_fixtures.FixtureTest, AssertsCompiledSQL): assert_raises(TypeError, Foo, x=5) assert_raises(TypeError, Bar, x=5) - def test_lru_cache_warning(self): - users = self.tables.users - User = self.classes.User - m = mapper(User, users) - - for i in range(149): - m._compiled_cache["key_%s" % i] = "foo" - - def go(): - m._compiled_cache["key_150"] = "foo" - m._compiled_cache["key_151"] = "foo" - - assert_raises_message( - sa.exc.SAWarning, - r"Compiled statement cache for mapper Mapper.User.users is " - "reaching its size threshold of 150, based on " - "_compiled_cache_size of 100. ", - go - ) - m._compiled_cache.size_alert = None - for i in range(152, 200): - m._compiled_cache["key_%d" % i] = "foo" - assert len(m._compiled_cache) < 150 - - def test_sort_states_comparisons(self): """test that _sort_states() doesn't compare insert_order to state.key, for set of mixed |