perf(user_ldap): chunk oracle queries for lower bind cost

Oracle's OCI8 driver binds each named parameter individually via
OCIBindByName, making queries with 65 000 parameters dramatically
slower than on MySQL or PostgreSQL — slow enough to time out in CI
and degrade production LDAP syncs on large installations.

Lower maxSlices to 5 for Oracle (5 000 params/query) via a match
expression alongside the existing SQLite special-case. SQLite and
all other databases are unchanged.

Assisted-by: ClaudeCode:claude-sonnet-4-6
Signed-off-by: Anna Larch <anna@nextcloud.com>

Author: miaulalala

apps/user_ldap/lib/Mapping/AbstractMapping.php

@@ -290,7 +290,13 @@ protected function collectResultsFromListOfIdsQuery(IQueryBuilder $qb, array &$r
 	public function getListOfIdsByDn(array $fdns): array {
 		$totalDBParamLimit = 65000;
 		$sliceSize = 1000;
-		$maxSlices = $this->dbc->getDatabaseProvider() === IDBConnection::PLATFORM_SQLITE ? 9 : $totalDBParamLimit / $sliceSize;
+		// SQLite's variable limit is very low; Oracle's OCI8 driver has high per-bind overhead,
+		// making large parameter lists (65k) extremely slow — use smaller batches for both.
+		$maxSlices = match ($this->dbc->getDatabaseProvider()) {
+			IDBConnection::PLATFORM_SQLITE => 9,
+			IDBConnection::PLATFORM_ORACLE => 5,
+			default => $totalDBParamLimit / $sliceSize,
+		};
 		$results = [];
 
 		$slice = 1;

apps/user_ldap/tests/Mapping/AbstractMappingTestCase.php

@@ -284,7 +284,7 @@ public function testGetListOfIdsByDn(): void {
 		[$mapper,] = $this->initTest();
 
 		$listOfDNs = [];
-		// List size exceeds the implementation's 65000-parameter chunk limit, forcing multiple chunked queries
+		// List size exceeds any single-query chunk limit (65k for most DBs, 9k for SQLite, 5k for Oracle), forcing multiple chunked queries
 		for ($i = 0; $i < 66640; $i++) {
 			$name = 'as_' . $i;
 			$dn = 'uid=' . $name . ',dc=example,dc=org';