- Some default hash table sizes were tweaked, some upwards, some downwards.

3.1.0a1's tables resulted in a reduction in default server memory use.
  The new selected values provide more of a zero sum (increasing the size
  of tables likely to be populated, decreasing the size of tables unlikely).

- Lease structures appear in three spearate hashes: by IP address, by UID,
  and by hardware address.  One type of table was used for all three, and
  improvements to IP address hashing were applied to all three (so UID and
  hardware addresses were treated like 4-byte integers).  There are now two
  types of tables, and the uid/hw hashes use functions more appropriate
  to their needs.

- The max-lease-misbalance percentage no longer causes scheduled rebalance
  runs to be skipped: it still governs the schedule, but every scheduled
  run will attempt balance.

[ISC-Bugs #16396]

includes/dhcpd.h

@@ -67,7 +67,8 @@ typedef struct hash_table universe_hash_t;
 typedef struct hash_table option_name_hash_t;
 typedef struct hash_table option_code_hash_t;
 typedef struct hash_table dns_zone_hash_t;
-typedef struct hash_table lease_hash_t;
+typedef struct hash_table lease_ip_hash_t;
+typedef struct hash_table lease_id_hash_t;
 typedef struct hash_table host_hash_t;
 typedef struct hash_table class_hash_t;
 
@@ -87,13 +88,23 @@ typedef struct hash_table class_hash_t;
 # define BYTE_CODE_HASH_SIZE	254	/* Default would be rediculous. */
 #endif
 
+/* Although it is highly improbable that a 16-bit option space might
+ * actually use 2^16 actual defined options, it is the worst case
+ * scenario we must prepare for.  Having 4 options per bucket in this
+ * case is pretty reasonable.
+ */
 #if !defined (WORD_NAME_HASH_SIZE)
-# define WORD_NAME_HASH_SIZE	0	/* Default. */
+# define WORD_NAME_HASH_SIZE	20479
 #endif
 #if !defined (WORD_CODE_HASH_SIZE)
-# define WORD_CODE_HASH_SIZE	0	/* Default. */
+# define WORD_CODE_HASH_SIZE	16384
 #endif
 
+/* Not only is it improbable that the 32-bit spaces might actually use 2^32
+ * defined options, it is infeasable.  It would be best for this kind of
+ * space to be dynamically sized.  Instead we size it at the word hash's
+ * level.
+ */
 #if !defined (QUAD_NAME_HASH_SIZE)
 # define QUAD_NAME_HASH_SIZE	WORD_NAME_HASH_SIZE
 #endif
@@ -111,15 +122,18 @@ typedef struct hash_table class_hash_t;
 #endif
 
 #if !defined (NWIP_HASH_SIZE)
-# define NWIP_HASH_SIZE		11	/* A really small table. */
+# define NWIP_HASH_SIZE		17	/* A really small table. */
 #endif
 
 #if !defined (FQDN_HASH_SIZE)
-# define FQDN_HASH_SIZE		7	/* A rediculously small table. */
+# define FQDN_HASH_SIZE		13	/* A rediculously small table. */
 #endif
 
+/* I really doubt a given installation is going to have more than a few
+ * hundred vendors involved.
+ */
 #if !defined (VIVCO_HASH_SIZE)
-# define VIVCO_HASH_SIZE	QUAD_CODE_HASH_SIZE
+# define VIVCO_HASH_SIZE	127
 #endif
 
 #if !defined (VIVSO_HASH_SIZE)
@@ -131,35 +145,52 @@ typedef struct hash_table class_hash_t;
 #endif
 
 #if !defined (UNIVERSE_HASH_SIZE)
-# define UNIVERSE_HASH_SIZE	11	/* A really small table. */
+# define UNIVERSE_HASH_SIZE	13	/* A really small table. */
 #endif
 
 #if !defined (GROUP_HASH_SIZE)
 # define GROUP_HASH_SIZE	0	/* Default. */
 #endif
 
+/* At least one person has indicated they use ~20k host records.
+ */
 #if !defined (HOST_HASH_SIZE)
-# define HOST_HASH_SIZE		0	/* Default. */
+# define HOST_HASH_SIZE		22501
 #endif
 
+/* We have user reports of use of ISC DHCP numbering leases in the 200k's.
+ *
+ * We also have reports of folks using 10.0/8 as a dynamic range.  The
+ * following is something of a compromise between the two.  At the ~2-3
+ * hundred thousand leases, there's ~2-3 leases to search in each bucket.
+ */
 #if !defined (LEASE_HASH_SIZE)
-# define LEASE_HASH_SIZE	0	/* Default. */
+# define LEASE_HASH_SIZE	100003
 #endif
 
+/* It is not known what the worst case subclass hash size is.  We estimate
+ * high, I think.
+ */
 #if !defined (SCLASS_HASH_SIZE)
-# define SCLASS_HASH_SIZE	1009	/* A less than gigantic sized table. */
+# define SCLASS_HASH_SIZE	12007
 #endif
 
 #if !defined (AGENT_HASH_SIZE)
 # define AGENT_HASH_SIZE	11	/* A really small table. */
 #endif
 
+/* The server hash size is used for both names and codes.  There aren't
+ * many (roughly 50 at the moment), so we use a smaller table.  If we
+ * use a 1:1 table size, then we get name collisions due to poor name
+ * hashing.  So we use double the space we need, which drastically
+ * reduces collisions.
+ */
 #if !defined (SERVER_HASH_SIZE)
-# define SERVER_HASH_SIZE	(sizeof(server_options) / sizeof(struct option))
+# define SERVER_HASH_SIZE (2*(sizeof(server_options) / sizeof(struct option)))
 #endif
 
 
-
+/* How many options are likely to appear in a single packet? */
 #if !defined (OPTION_HASH_SIZE)
 # define OPTION_HASH_SIZE 17
 # define OPTION_HASH_PTWO 32	/* Next power of two above option hash. */
@@ -1071,7 +1102,10 @@ HASH_FUNCTIONS_DECL (option_name, const char *, struct option,
 HASH_FUNCTIONS_DECL (option_code, const unsigned *, struct option,
 		     option_code_hash_t)
 HASH_FUNCTIONS_DECL (dns_zone, const char *, struct dns_zone, dns_zone_hash_t)
-HASH_FUNCTIONS_DECL (lease, const unsigned char *, struct lease, lease_hash_t)
+HASH_FUNCTIONS_DECL(lease_ip, const unsigned char *, struct lease,
+		    lease_ip_hash_t)
+HASH_FUNCTIONS_DECL(lease_id, const unsigned char *, struct lease,
+		    lease_id_hash_t)
 HASH_FUNCTIONS_DECL (host, const unsigned char *, struct host_decl, host_hash_t)
 HASH_FUNCTIONS_DECL (class, const char *, struct class, class_hash_t)
 
@@ -2536,9 +2570,9 @@ extern struct shared_network *shared_networks;
 extern host_hash_t *host_hw_addr_hash;
 extern host_hash_t *host_uid_hash;
 extern host_hash_t *host_name_hash;
-extern lease_hash_t *lease_uid_hash;
-extern lease_hash_t *lease_ip_addr_hash;
-extern lease_hash_t *lease_hw_addr_hash;
+extern lease_id_hash_t *lease_uid_hash;
+extern lease_ip_hash_t *lease_ip_addr_hash;
+extern lease_id_hash_t *lease_hw_addr_hash;
 
 extern omapi_object_type_t *dhcp_type_host;