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- If a client renews before 'dhcp-cache-threshold' percent of its lease

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has elapsed (default 25%), the server will reuse the allocated lease
  (provide a lease within the currently allocated lease-time) rather
  than extend or renew the lease.  This absolves the server of needing
  to perform an fsync() operation on the lease database before reply,
  which improves performance. [ISC-Bugs #22228]
This commit is contained in:
Tomek Mrugalski
2011-05-12 13:26:55 +00:00
parent c616de4f1e
commit 929a236497
5 changed files with 116 additions and 25 deletions
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7
RELNOTES
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@@ -141,6 +141,13 @@ work on other platforms. Please report any problems and suggested fixes to
- Compilation problem with gcc4.5 and omshell.c resolved. [ISC-Bugs #23831]
- If a client renews before 'dhcp-cache-threshold' percent of its lease
has elapsed (default 25%), the server will reuse the allocated lease
(provide a lease within the currently allocated lease-time) rather
than extend or renew the lease. This absolves the server of needing
to perform an fsync() operation on the lease database before reply,
which improves performance. [ISC-Bugs #22228]
Changes since 4.2.0
- Documentation cleanup covering multiple tickets

46
includes/dhcpd.h
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@@ -691,27 +691,6 @@ struct lease_state {
#define SV_LIMIT_PREFS_PER_IA 57
#define SV_DELAYED_ACK 58
#define SV_MAX_ACK_DELAY 59
#if !defined (DEFAULT_PING_TIMEOUT)
# define DEFAULT_PING_TIMEOUT 1
#endif
#if !defined (DEFAULT_DELAYED_ACK)
# define DEFAULT_DELAYED_ACK 28 /* default SO_SNDBUF size / 576 bytes */
#endif
#if !defined (DEFAULT_ACK_DELAY_SECS)
# define DEFAULT_ACK_DELAY_SECS 0
#endif
#if !defined (DEFAULT_ACK_DELAY_USECS)
# define DEFAULT_ACK_DELAY_USECS 250000 /* 1/4 of a second */
#endif
#if !defined (DEFAULT_MIN_ACK_DELAY_USECS)
# define DEFAULT_MIN_ACK_DELAY_USECS 10000 /* 1/100 second */
#endif
#if defined(LDAP_CONFIGURATION)
# define SV_LDAP_SERVER 60
# define SV_LDAP_PORT 61
@@ -734,6 +713,31 @@ struct lease_state {
# define SV_LDAP_TLS_RANDFILE 77
#endif
#endif
#define SV_CACHE_THRESHOLD 78
#if !defined (DEFAULT_PING_TIMEOUT)
# define DEFAULT_PING_TIMEOUT 1
#endif
#if !defined (DEFAULT_DELAYED_ACK)
# define DEFAULT_DELAYED_ACK 28 /* default SO_SNDBUF size / 576 bytes */
#endif
#if !defined (DEFAULT_ACK_DELAY_SECS)
# define DEFAULT_ACK_DELAY_SECS 0
#endif
#if !defined (DEFAULT_ACK_DELAY_USECS)
# define DEFAULT_ACK_DELAY_USECS 250000 /* 1/4 of a second */
#endif
#if !defined (DEFAULT_MIN_ACK_DELAY_USECS)
# define DEFAULT_MIN_ACK_DELAY_USECS 10000 /* 1/100 second */
#endif
#if !defined (DEFAULT_CACHE_THRESHOLD)
# define DEFAULT_CACHE_THRESHOLD 25
#endif
#if !defined (DEFAULT_DEFAULT_LEASE_TIME)
# define DEFAULT_DEFAULT_LEASE_TIME 43200

61
server/dhcp.c
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@@ -1502,6 +1502,10 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
struct in_addr from;
TIME remaining_time;
struct iaddr cip;
#if defined(DELAYED_ACK)
isc_boolean_t enqueue = ISC_TRUE;
#endif
int use_old_lease = 0;
unsigned i, j;
int s1;
@@ -2445,6 +2449,48 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
packet -> raw -> chaddr,
sizeof packet -> raw -> chaddr); /* XXX */
} else {
int commit = (!offer || (offer == DHCPACK));
int thresh = DEFAULT_CACHE_THRESHOLD;
/*
* Check if the lease was issued recently, if so replay the
* current lease and do not require a database sync event.
* Recently is defined as being issued less than a given
* percentage of the lease previously. The percentage can be
* chosen either from a default value or via configuration.
*
*/
if ((oc = lookup_option(&server_universe, state->options,
SV_CACHE_THRESHOLD)) &&
evaluate_option_cache(&d1, packet, lt, NULL,
packet->options, state->options,
&lt->scope, oc, MDL)) {
if (d1.len == 1 &&
(d1.data[0] >= 0) && (d1.data[0] < 100))
thresh = d1.data[0];
data_string_forget(&d1, MDL);
}
if ((thresh > 0) && (offer == DHCPACK) &&
(lease->binding_state == FTS_ACTIVE)) {
int limit;
int prev_lease = lease->ends - lease->starts;
/* it is better to avoid division by 0 */
if (prev_lease <= (INT_MAX / thresh))
limit = prev_lease * thresh / 100;
else
limit = prev_lease / 100 * thresh;
if ((lt->starts - lease->starts) <= limit) {
lt->starts = lease->starts;
state->offered_expiry = lt->ends = lease->ends;
commit = 0;
use_old_lease = 1;
}
}
#if !defined(DELAYED_ACK)
/* Install the new information on 'lt' onto the lease at
* 'lease'. If this is a DHCPOFFER, it is a 'soft' promise,
@@ -2454,9 +2500,19 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
* the same lease to another client later, and that would be
* a conflict.
*/
if (!supersede_lease(lease, lt, !offer || (offer == DHCPACK),
if (!use_old_lease && !supersede_lease(lease, lt, commit,
offer == DHCPACK, offer == DHCPACK)) {
#else /* defined(DELAYED_ACK) */
/*
* If there already isn't a need for a lease commit, and we
* can just answer right away, set a flag to indicate this.
*/
if (commit && !(lease->flags & STATIC_LEASE) &&
(!offer || (offer == DHCPACK)))
enqueue = ISC_TRUE;
else
enqueue = ISC_FALSE;
/* Install the new information on 'lt' onto the lease at
* 'lease'.  We will not 'commit' this information to disk
* yet (fsync()), we will 'propogate' the information if
@@ -2865,8 +2921,7 @@ void ack_lease (packet, lease, offer, when, msg, ms_nulltp, hp)
} else {
lease->cltt = cur_time;
#if defined(DELAYED_ACK)
if (!(lease->flags & STATIC_LEASE) &&
(!offer || (offer == DHCPACK)))
if (enqueue)
delayed_ack_enqueue(lease);
else
#endif

26
server/dhcpd.conf.5
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@@ -27,7 +27,7 @@
.\" Support and other services are available for ISC products - see
.\" https://www.isc.org for more information or to learn more about ISC.
.\"
.\" $Id: dhcpd.conf.5,v 1.109 2011/04/25 23:43:16 sar Exp $
.\" $Id: dhcpd.conf.5,v 1.110 2011/05/12 13:26:55 tomasz Exp $
.\"
.TH dhcpd.conf 5
.SH NAME
@@ -2159,6 +2159,30 @@ with \'./configure --enable-delayed-ack\'.
.RE
.PP
The
.I dhcp-cache-threshold
statement
.RS 0.25i
.PP
.B dhcp-cache-threshold \fIpercentage\fB;\fR
.PP
The \fIdhcp-cache-threshold\fR statement takes one integer parameter
with allowed values between 0 and 100. The default value is 25 (25% of
the lease time). This parameter expresses the percentage of the total
lease time, measured from the beginning, during which a
client's attempt to renew its lease will result in getting
the already assigned lease, rather than an extended lease.
.PP
Clients that attempt renewal frequently can cause the server to
update and write the database frequently resulting in a performance
impact on the server. The \fIdhcp-cache-threshold\fR
statement instructs the DHCP server to avoid updating leases too
frequently thus avoiding this behavior. Instead the server assigns the
same lease with no modifications except for CLTT (Client Last
Transmission Time) which does not require disk operations. This
feature applies to IPv4 only.
.RE
.PP
The
.I do-forward-updates
statement
.RS 0.25i

1
server/stables.c
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@@ -266,6 +266,7 @@ static struct option server_options[] = {
{ "ldap-tls-randfile", "t", &server_universe, 77, 1 },
#endif /* LDAP_USE_SSL */
#endif /* LDAP_CONFIGURATION */
{ "dhcp-cache-threshold", "B", &server_universe, 78, 1 },
{ NULL, NULL, NULL, 0, 0 }
};