Pause the dbiterator when dumping the zone to the disk

When we rewrote the zone dumping to use the separate threadpool, the
dumping would acquire the read lock for the whole time the zone dumping
process is dumping the zone.

When combined with incoming IXFR that tries to acquire the write lock on
the same rwlock, we would end up blocking all the other readers.

In this commit, we pause the dbiterator every time we get next record
and before start dumping it to the disk.

diff --git a/lib/dns/masterdump.c b/lib/dns/masterdump.c
index c5f00bd1c3301edee3d4aaeeb09ec59eed90d9f7..31304380d47696162b513d04cc302d0f9eaeed2d 100644 (file)
--- a/lib/dns/masterdump.c
+++ b/lib/dns/masterdump.c
@@ -254,7 +254,6 @@ struct dns_dumpctx {
        isc_mutex_t lock;
        isc_refcount_t references;
        atomic_bool canceled;
-       bool first;
        bool do_date;
        isc_stdtime_t now;
        FILE *f;
@@ -1578,7 +1577,6 @@ dumpctx_create(isc_mem_t *mctx, dns_db_t *db, dns_dbversion_t *version,
        dctx->done = NULL;
        dctx->done_arg = NULL;
        dctx->task = NULL;
-       dctx->first = true;
        atomic_init(&dctx->canceled, false);
        dctx->file = NULL;
        dctx->tmpfile = NULL;
@@ -1737,7 +1735,6 @@ dumptostream(dns_dumpctx_t *dctx) {
        char *bufmem;
        dns_name_t *name;
        dns_fixedname_t fixname;
-       isc_time_t start;
 
        bufmem = isc_mem_get(dctx->mctx, initial_buffer_length);
 
@@ -1745,32 +1742,24 @@ dumptostream(dns_dumpctx_t *dctx) {
 
        name = dns_fixedname_initname(&fixname);
 
-       if (dctx->first) {
-               CHECK(writeheader(dctx));
+       CHECK(writeheader(dctx));
 
-               /*
-                * Fast format is not currently written incrementally,
-                * so we make the call to dns_db_serialize() here.
-                * If the database is anything other than an rbtdb,
-                * this should result in not implemented
-                */
-               if (dctx->format == dns_masterformat_map) {
-                       result = dns_db_serialize(dctx->db, dctx->version,
-                                                 dctx->f);
-                       goto cleanup;
-               }
-
-               result = dns_dbiterator_first(dctx->dbiter);
-               if (result != ISC_R_SUCCESS && result != ISC_R_NOMORE) {
-                       goto cleanup;
-               }
+       /*
+        * Fast format is not currently written incrementally,
+        * so we make the call to dns_db_serialize() here.
+        * If the database is anything other than an rbtdb,
+        * this should result in not implemented
+        */
+       if (dctx->format == dns_masterformat_map) {
+               result = dns_db_serialize(dctx->db, dctx->version, dctx->f);
+               goto cleanup;
+       }
 
-               dctx->first = false;
-       } else {
-               result = ISC_R_SUCCESS;
+       result = dns_dbiterator_first(dctx->dbiter);
+       if (result != ISC_R_SUCCESS && result != ISC_R_NOMORE) {
+               goto cleanup;
        }
 
-       isc_time_now(&start);
        while (result == ISC_R_SUCCESS) {
                dns_rdatasetiter_t *rdsiter = NULL;
                dns_dbnode_t *node = NULL;
@@ -1790,6 +1779,10 @@ dumptostream(dns_dumpctx_t *dctx) {
                        }
                        dctx->tctx.neworigin = origin;
                }
+
+               result = dns_dbiterator_pause(dctx->dbiter);
+               RUNTIME_CHECK(result == ISC_R_SUCCESS);
+
                result = dns_db_allrdatasets(dctx->db, node, dctx->version,
                                             dctx->now, &rdsiter);
                if (result != ISC_R_SUCCESS) {