rearchitect reflection for batched performance

Rearchitected the schema reflection API to allow some dialects to make use
of high performing batch queries to reflect the schemas of many tables at
once using much fewer queries. The new performance features are targeted
first at the PostgreSQL and Oracle backends, and may be applied to any
dialect that makes use of SELECT queries against system catalog tables to
reflect tables (currently this omits the MySQL and SQLite dialects which
instead make use of parsing the "CREATE TABLE" statement, however these
dialects do not have a pre-existing performance issue with reflection. MS
SQL Server is still a TODO).

The new API is backwards compatible with the previous system, and should
require no changes to third party dialects to retain compatibility;
third party dialects can also opt into the new system by implementing
batched queries for schema reflection.

Along with this change is an updated reflection API that is fully
:pep:`484` typed, features many new methods and some changes.

Fixes: #4379
Change-Id: I897ec09843543aa7012bcdce758792ed3d415d08

1 files changed, 38 insertions, 0 deletions

diff --git a/lib/sqlalchemy/sql/cache_key.py b/lib/sqlalchemy/sql/cache_key.py
index c16fbdae1..5922c2db0 100644
--- a/lib/sqlalchemy/sql/cache_key.py
+++ b/lib/sqlalchemy/sql/cache_key.py
@@ -12,6 +12,7 @@ from itertools import zip_longest
 import typing
 from typing import Any
 from typing import Dict
+from typing import Iterable
 from typing import Iterator
 from typing import List
 from typing import MutableMapping
@@ -546,6 +547,43 @@ class CacheKey(NamedTuple):
         return target_element.params(translate)
 
 
+def _ad_hoc_cache_key_from_args(
+    tokens: Tuple[Any, ...],
+    traverse_args: Iterable[Tuple[str, InternalTraversal]],
+    args: Iterable[Any],
+) -> Tuple[Any, ...]:
+    """a quick cache key generator used by reflection.flexi_cache."""
+    bindparams: List[BindParameter[Any]] = []
+
+    _anon_map = anon_map()
+
+    tup = tokens
+
+    for (attrname, sym), arg in zip(traverse_args, args):
+        key = sym.name
+        visit_key = key.replace("dp_", "visit_")
+
+        if arg is None:
+            tup += (attrname, None)
+            continue
+
+        meth = getattr(_cache_key_traversal_visitor, visit_key)
+        if meth is CACHE_IN_PLACE:
+            tup += (attrname, arg)
+        elif meth in (
+            CALL_GEN_CACHE_KEY,
+            STATIC_CACHE_KEY,
+            ANON_NAME,
+            PROPAGATE_ATTRS,
+        ):
+            raise NotImplementedError(
+                f"Haven't implemented symbol {meth} for ad-hoc key from args"
+            )
+        else:
+            tup += meth(attrname, arg, None, _anon_map, bindparams)
+    return tup
+
+
 class _CacheKeyTraversal(HasTraversalDispatch):
     # very common elements are inlined into the main _get_cache_key() method
     # to produce a dramatic savings in Python function call overhead