feat(api): avoid caching already concrete tables

ibis/backends/__init__.py

@@ -805,17 +805,22 @@ def _cached_table(self, table: ir.Table) -> ir.CachedTable:
             Cached table
         """
         entry = self._cache_op_to_entry.get(table.op())
-        if entry is None or (cached_op := entry.cached_op_ref()) is None:
-            cached_op = self._create_cached_table(util.gen_name("cached"), table).op()
-            entry = CacheEntry(
-                table.op(),
-                weakref.ref(cached_op),
-                weakref.finalize(
-                    cached_op, self._finalize_cached_table, cached_op.name
-                ),
-            )
-            self._cache_op_to_entry[table.op()] = entry
-            self._cache_name_to_entry[cached_op.name] = entry
+        if entry is not None and (cached_op := entry.cached_op_ref()) is not None:
+            # Entry was already cached
+            return ir.CachedTable(cached_op)
+
+        if not self._should_cache_table_expr(table):
+            # Expression isn't worth caching, no-op
+            return ir.CachedTable(table.op())
+
+        cached_op = self._create_cached_table(util.gen_name("cached"), table).op()
+        entry = CacheEntry(
+            table.op(),
+            weakref.ref(cached_op),
+            weakref.finalize(cached_op, self._finalize_cached_table, cached_op.name),
+        )
+        self._cache_op_to_entry[table.op()] = entry
+        self._cache_name_to_entry[cached_op.name] = entry
         return ir.CachedTable(cached_op)
 
     def _finalize_cached_table(self, name: str) -> None:
@@ -838,6 +843,31 @@ def _finalize_cached_table(self, name: str) -> None:
                 if not sys.is_finalizing():
                     raise
 
+    def _should_cache_table_expr(self, expr: ir.Table) -> bool:
+        """Checks if a given table expression is worth caching."""
+        op = expr.op()
+
+        # Don't cache if an expression is a column subselection of a physical table.
+        while isinstance(op, (ops.Project, ops.DropColumns)):
+            if isinstance(op, ops.Project) and not all(
+                isinstance(v, ops.Field) for v in op.values.values()
+            ):
+                return True
+            op = op.parent
+
+        return not isinstance(
+            op, ops.PhysicalTable
+        ) or self._should_cache_physical_table(op)
+
+    def _should_cache_physical_table(self, op: ops.PhysicalTable) -> bool:
+        """Check whether a PhysicalTable node is worth caching.
+
+        By default we don't cache any PhysicalTable ops. Some backends need
+        to override this method to allow for caching of tables backed by
+        potentially expensive IO (e.g. a TEMP VIEW backed by data on S3).
+        """
+        return False
+
     def _create_cached_table(self, name: str, expr: ir.Table) -> ir.Table:
         return self.create_table(name, expr, schema=expr.schema(), temp=True)
 

ibis/backends/duckdb/__init__.py

@@ -1589,6 +1589,24 @@ def _get_schema_using_query(self, query: str) -> sch.Schema:
             }
         )
 
+    def _should_cache_physical_table(self, op: ops.PhysicalTable) -> bool:
+        if isinstance(op, (ops.DatabaseTable, ops.UnboundTable)):
+            # Cache temp views since they're used for `read_csv`/`read_parquet`
+            # and may point to remote data, don't cache anything else.
+            sql = (
+                sg.select(sg.func("any_value", C.table_type.eq("VIEW")))
+                .from_(sg.table("tables", db="information_schema"))
+                .where(
+                    C.table_catalog.eq(op.namespace.catalog or self.current_catalog),
+                    C.table_schema.eq(op.namespace.database or self.current_database),
+                )
+                .sql(self.dialect)
+            )
+            with self._safe_raw_sql(sql) as cur:
+                result = cur.fetchone()
+            return True if result is None else result[0]
+        return False
+
     def _register_in_memory_table(self, op: ops.InMemoryTable) -> None:
         name = op.name
         try:

ibis/backends/pyspark/__init__.py

@@ -721,6 +721,25 @@ def _drop_cached_table(self, name):
         t.unpersist()
         assert not t.is_cached
 
+    def _should_cache_physical_table(self, op: ops.PhysicalTable) -> bool:
+        if isinstance(op, (ops.DatabaseTable, ops.UnboundTable)):
+            # Cache temp views since they're used for `read_csv`/`read_parquet`
+            # and may point to remote data, don't cache anything else.
+            sql = (
+                f"SHOW VIEWS IN {op.namespace.database}"
+                if op.namespace.database
+                else "SHOW VIEWS"
+            )
+            with self._active_catalog(op.namespace.catalog):
+                for view in self._session.sql(sql).collect():
+                    if view.viewName == op.name:
+                        # already cached tables are also exposed as temp views,
+                        # check the view isn't backed by the cache
+                        return (
+                            view.isTemporary and op.name not in self._cached_dataframes
+                        )
+        return False
+
     def read_delta(
         self,
         path: str | Path,

ibis/expr/types/relations.py

@@ -4900,7 +4900,8 @@ def __enter__(self):
     def release(self):
         """Release the underlying expression from the cache."""
         current_backend = self._find_backend(use_default=True)
-        return current_backend._finalize_cached_table(self.op().name)
+        if isinstance(op := self.op(), ops.PhysicalTable):
+            current_backend._finalize_cached_table(op.name)
 
 
 public(Table=Table, CachedTable=CachedTable)