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Add "-T maxcachesize=..." command line option

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An implicit default of "max-cache-size 90%;" may cause memory use issues
on hosts which run numerous named instances in parallel (e.g. GitLab CI
runners) due to the cache RBT hash table now being pre-allocated [1] at
startup.  Add a new command line option, "-T maxcachesize=...", to allow
the default value of "max-cache-size" to be overridden at runtime.  When
this new option is in effect, it overrides any other "max-cache-size"
setting in the configuration, either implicit or explicit.  This
approach was chosen because it is arguably the simplest one to
implement.

The following alternative approaches to solving this problem were
considered and ultimately rejected (after it was decided they were not
worth the extra code complexity):

  - adding the same command line option, but making explicit
    configuration statements have priority over it,

  - adding a build-time option that allows the implicit default of
    "max-cache-size 90%;" to be overridden.

[1] see commit e24bc324b4
This commit is contained in:
Michał Kępień 2020-08-31 13:15:33 +02:00
parent 96c4010fe5
commit 9ac1f6a9bc
3 changed files with 13 additions and 1 deletions
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1
bin/named/include/named/globals.h
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@ -143,6 +143,7 @@ EXTERN bool named_g_memstatistics INIT(false);
EXTERN bool named_g_keepstderr INIT(false);
EXTERN unsigned int named_g_tat_interval INIT(24 * 3600);
EXTERN unsigned int named_g_maxcachesize INIT(0);
#if defined(HAVE_GEOIP2)
EXTERN dns_geoip_databases_t *named_g_geoip INIT(NULL);

2
bin/named/main.c
View file

@ -650,6 +650,8 @@ parse_T_opt(char *option) {
named_g_nosyslog = true;
} else if (!strcmp(option, "notcp")) {
notcp = true;
} else if (!strncmp(option, "maxcachesize=", 13)) {
named_g_maxcachesize = atoi(option + 13);
} else if (!strcmp(option, "maxudp512")) {
maxudp = 512;
} else if (!strcmp(option, "maxudp1460")) {

11
bin/named/server.c
View file

@ -4114,7 +4114,16 @@ configure_view(dns_view_t *view, dns_viewlist_t *viewlist, cfg_obj_t *config,
obj = NULL;
result = named_config_get(maps, "max-cache-size", &obj);
INSIST(result == ISC_R_SUCCESS);
if (cfg_obj_isstring(obj)) {
/*
* If "-T maxcachesize=..." is in effect, it overrides any other
* "max-cache-size" setting found in configuration, either implicit or
* explicit. For simplicity, the value passed to that command line
* option is always treated as the number of bytes to set
* "max-cache-size" to.
*/
if (named_g_maxcachesize != 0) {
max_cache_size = named_g_maxcachesize;
} else if (cfg_obj_isstring(obj)) {
str = cfg_obj_asstring(obj);
INSIST(strcasecmp(str, "unlimited") == 0);
max_cache_size = 0;