From 22deafe15289d2be55682e1632016004b02b62c0 Mon Sep 17 00:00:00 2001 From: Mike Bayer Date: Fri, 3 Dec 2021 14:04:05 -0500 Subject: Warn when caching is disabled / document This patch adds new warnings for all elements that don't indicate their caching behavior, including user-defined ClauseElement subclasses and third party dialects. it additionally adds new documentation to discuss an apparent performance degradation in 1.4 when caching is disabled as a result in the significant expense incurred by ORM lazy loaders, which in 1.3 used BakedQuery so were actually cached. As a result of adding the warnings, a fair degree of lesser used SQL expression objects identified that they did not define caching behavior so would have been producing ``[no key]``, including PostgreSQL constructs ``hstore`` and ``array``. These have been amended to use inherit cache where appropriate. "on conflict" constructs in PostgreSQL, MySQL, SQLite still explicitly don't generate a cache key at this time. The change also adds a test for all constructs via assert_compile() to assert they will not generate cache warnings. Fixes: #7394 Change-Id: I85958affbb99bfad0f5efa21bc8f2a95e7e46981 --- lib/sqlalchemy/engine/default.py | 21 +++++++++++++++++---- 1 file changed, 17 insertions(+), 4 deletions(-) (limited to 'lib/sqlalchemy/engine/default.py') diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py index 9574e9980..e91e34f00 100644 --- a/lib/sqlalchemy/engine/default.py +++ b/lib/sqlalchemy/engine/default.py @@ -321,10 +321,23 @@ class DefaultDialect(interfaces.Dialect): @util.memoized_property def _supports_statement_cache(self): - return ( - self.__class__.__dict__.get("supports_statement_cache", False) - is True - ) + ssc = self.__class__.__dict__.get("supports_statement_cache", None) + if ssc is None: + util.warn( + "Dialect %s:%s will not make use of SQL compilation caching " + "as it does not set the 'supports_statement_cache' attribute " + "to ``True``. This can have " + "significant performance implications including some " + "performance degradations in comparison to prior SQLAlchemy " + "versions. Dialect maintainers should seek to set this " + "attribute to True after appropriate development and testing " + "for SQLAlchemy 1.4 caching support. Alternatively, this " + "attribute may be set to False which will disable this " + "warning." % (self.name, self.driver), + code="cprf", + ) + + return bool(ssc) @util.memoized_property def _type_memos(self): -- cgit v1.2.1