Make query chain processing asynchronous

Under some circumstances when processing a query response - for example,
when it contains a CNAME or DNAME - a query will have to be restarted
from the beginning to look up a new target.

This was previously handled by recursively calling the ns__query_start()
function directly from ns_query_done(). However, performance test data
indicated that chains of CNAMEs could consume quite a bit of time inside
the worker thread, increasing latency for other waiting queries.  This
has now been changed so that restarted queries are run asynchronously.

diff --git a/lib/ns/query.c b/lib/ns/query.c
index 87591f7d696e534cf64a21193b8456432f56bcbc..7349582004339c6f9f89cf62ff1f27f86bc3f184 100644 (file)
--- a/lib/ns/query.c
+++ b/lib/ns/query.c
@@ -19,6 +19,7 @@
 #include <stdint.h>
 #include <string.h>
 
+#include <isc/async.h>
 #include <isc/hex.h>
 #include <isc/mem.h>
 #include <isc/once.h>
@@ -406,7 +407,7 @@ qctx_freedata(query_ctx_t *qctx);
 static void
 qctx_destroy(query_ctx_t *qctx);
 
-static isc_result_t
+static void
 query_setup(ns_client_t *client, dns_rdatatype_t qtype);
 
 static isc_result_t
@@ -5512,7 +5513,7 @@ query_trace(query_ctx_t *qctx) {
  * ns__query_start() again with the same query context. Resuming from
  * recursion is handled by query_resume().
  */
-static isc_result_t
+static void
 query_setup(ns_client_t *client, dns_rdatatype_t qtype) {
        isc_result_t result = ISC_R_UNSET;
        query_ctx_t qctx;
@@ -5527,15 +5528,13 @@ query_setup(ns_client_t *client, dns_rdatatype_t qtype) {
         */
        result = ns__query_sfcache(&qctx);
        if (result != ISC_R_COMPLETE) {
-               qctx_destroy(&qctx);
-               return (result);
+               goto cleanup;
        }
 
-       result = ns__query_start(&qctx);
+       (void)ns__query_start(&qctx);
 
 cleanup:
        qctx_destroy(&qctx);
-       return (result);
 }
 
 static bool
@@ -5833,6 +5832,19 @@ cleanup:
        return (result);
 }
 
+static void
+async_restart(void *arg) {
+       query_ctx_t *qctx = arg;
+       ns_client_t *client = qctx->client;
+
+       ns__query_start(qctx);
+
+       qctx_clean(qctx);
+       qctx_freedata(qctx);
+       qctx_destroy(qctx);
+       isc_mem_put(client->manager->mctx, qctx, sizeof(*qctx));
+}
+
 /*
  * Allocate buffers in 'qctx' used to store query results.
  *
@@ -6834,7 +6846,7 @@ query_hookresume(void *arg) {
        } else {
                switch (rev->hookpoint) {
                case NS_QUERY_SETUP:
-                       (void)query_setup(client, qctx->qtype);
+                       query_setup(client, qctx->qtype);
                        break;
                case NS_QUERY_START_BEGIN:
                        (void)ns__query_start(qctx);
@@ -10387,7 +10399,7 @@ query_cname(query_ctx_t *qctx) {
 
        result = query_zerottl_refetch(qctx);
        if (result != ISC_R_COMPLETE) {
-               return (result);
+               goto cleanup;
        }
 
        /*
@@ -10441,7 +10453,8 @@ query_cname(query_ctx_t *qctx) {
        result = dns_rdataset_first(trdataset);
        if (result != ISC_R_SUCCESS) {
                dns_message_puttempname(qctx->client->message, &tname);
-               return (ns_query_done(qctx));
+               (void)ns_query_done(qctx);
+               goto cleanup;
        }
 
        dns_rdataset_current(trdataset, &rdata);
@@ -10538,7 +10551,8 @@ query_dname(query_ctx_t *qctx) {
        result = dns_rdataset_first(trdataset);
        if (result != ISC_R_SUCCESS) {
                dns_message_puttempname(qctx->client->message, &tname);
-               return (ns_query_done(qctx));
+               (void)ns_query_done(qctx);
+               goto cleanup;
        }
 
        dns_rdataset_current(trdataset, &rdata);
@@ -10570,7 +10584,8 @@ query_dname(query_ctx_t *qctx) {
                qctx->client->message->rcode = dns_rcode_yxdomain;
        }
        if (result != ISC_R_SUCCESS) {
-               return (ns_query_done(qctx));
+               (void)ns_query_done(qctx);
+               goto cleanup;
        }
 
        ns_client_keepname(qctx->client, qctx->fname, qctx->dbuf);
@@ -10692,7 +10707,7 @@ query_prepresponse(query_ctx_t *qctx) {
 
        result = query_zerottl_refetch(qctx);
        if (result != ISC_R_COMPLETE) {
-               return (result);
+               goto cleanup;
        }
 
        return (query_respond(qctx));
@@ -11580,8 +11595,14 @@ ns_query_done(query_ctx_t *qctx) {
         * Do we need to restart the query (e.g. for CNAME chaining)?
         */
        if (qctx->want_restart && qctx->client->query.restarts < MAX_RESTARTS) {
+               query_ctx_t *saved_qctx = NULL;
                qctx->client->query.restarts++;
-               return (ns__query_start(qctx));
+               saved_qctx = isc_mem_get(qctx->client->manager->mctx,
+                                        sizeof(*saved_qctx));
+               qctx_save(qctx, saved_qctx);
+               isc_async_run(qctx->client->manager->loop, async_restart,
+                             saved_qctx);
+               return (DNS_R_CONTINUE);
        }
 
        if (qctx->result != ISC_R_SUCCESS &&
@@ -12124,5 +12145,5 @@ ns_query_start(ns_client_t *client, isc_nmhandle_t *handle) {
                message->flags |= DNS_MESSAGEFLAG_AD;
        }
 
-       (void)query_setup(client, qtype);
+       query_setup(client, qtype);
 }