Set the id2entry database pagesize to BDB_ID2ENTRY_PAGESIZE to avoid

overflow/fragmentation. (This is now 16K vs default 4K.) It turns out
that the entries' on-disk format is quite space-inefficient, storing
4 bytes per pointer or integer when typically >50% of those bytes are
zero. Oh well. It's about a 2:1 space increase over ldbm now, vs 4:1
before when all the entries were overflowing the 4K pages.

servers/slapd/back-bdb/back-bdb.h

@@ -44,6 +44,15 @@ LDAP_BEGIN_DECL
 #define BDB_DN2ID		1
 #define BDB_NDB			2
 
+/* The bdb on-disk entry format is pretty space-inefficient. Average
+ * sized user entries are 3-4K each. You need at least two entries to
+ * fit into a single database page, more is better. 64K is BDB's
+ * upper bound.
+ */
+#ifndef BDB_ID2ENTRY_PAGESIZE
+#define	BDB_ID2ENTRY_PAGESIZE	16384
+#endif
+
 #define BDB_INDICES		128
 
 struct bdb_db_info {

servers/slapd/back-bdb/init.c

@@ -232,10 +232,12 @@ bdb_db_open( BackendDB *be )
 		if( i == BDB_ID2ENTRY ) {
 			rc = db->bdi_db->set_bt_compare( db->bdi_db,
 				bdb_bt_compare );
+			rc = db->bdi_db->set_pagesize( db->bdi_db,
+				BDB_ID2ENTRY_PAGESIZE );
 		}
 		rc = db->bdi_db->open( db->bdi_db,
 			bdbi_databases[i].file,
-			bdbi_databases[i].name,
+		/*	bdbi_databases[i].name, */ NULL,
 			bdbi_databases[i].type,
 			bdbi_databases[i].flags | flags,
 			bdb->bi_dbenv_mode );