detect if the disk cannot keep up with data collection (netdata#7139)

* Adjust dbengine flushing speed more dynamically

* Added error tracking statistics for failure to flush events

* Added alarm for dbengine flushing errors

* Improved dbengine accounting for commited to be written pages

Author: mfundul

configs.signatures

@@ -381,7 +381,7 @@ declare -A configs_signatures=(
   ['7deb236ec68a512b9bdd18e6a51d76f7']='python.d/mysql.conf'
   ['7e5fc1644aa7a54f9dbb1bd102521b09']='health.d/memcached.conf'
   ['7f13631183fbdf79c21c8e5a171e9b34']='health.d/zfs.conf'
-  ['e48b89d4a97b96acf9a88970ab858c3b']='health.d/dbengine.conf'
+  ['8edc8c73a8f3ca40b32e27fe452c70f3']='health.d/dbengine.conf'
   ['7fb8184d56a27040e73261ed9c6fc76f']='health_alarm_notify.conf'
   ['80266bddd3df374923c750a6de91d120']='health.d/apache.conf'
   ['803a7f9dcb942eeac0fd764b9e3e38ca']='fping.conf'

daemon/global_statistics.c

@@ -544,7 +544,7 @@ void global_statistics_charts(void) {
         if (host->rrd_memory_mode == RRD_MEMORY_MODE_DBENGINE) {
             ++hosts_with_dbengine;
             /* get localhost's DB engine's statistics */
-            rrdeng_get_33_statistics(host->rrdeng_ctx, local_stats_array);
+            rrdeng_get_35_statistics(host->rrdeng_ctx, local_stats_array);
             for (i = 0 ; i < RRDENG_NR_STATS ; ++i) {
                 /* aggregate statistics across hosts */
                 stats_array[i] += local_stats_array[i];
@@ -775,6 +775,7 @@ void global_statistics_charts(void) {
             static RRDSET *st_errors = NULL;
             static RRDDIM *rd_fs_errors = NULL;
             static RRDDIM *rd_io_errors = NULL;
+            static RRDDIM *rd_flushing_errors = NULL;
 
             if (unlikely(!st_errors)) {
                 st_errors = rrdset_create_localhost(
@@ -794,12 +795,14 @@ void global_statistics_charts(void) {
 
                 rd_io_errors = rrddim_add(st_errors, "I/O errors", NULL, 1, 1, RRD_ALGORITHM_INCREMENTAL);
                 rd_fs_errors = rrddim_add(st_errors, "FS errors", NULL, 1, 1, RRD_ALGORITHM_INCREMENTAL);
+                rd_flushing_errors = rrddim_add(st_errors, "flushing errors", NULL, 1, 1, RRD_ALGORITHM_INCREMENTAL);
             }
             else
                 rrdset_next(st_errors);
 
             rrddim_set_by_pointer(st_errors, rd_io_errors, (collected_number)stats_array[30]);
             rrddim_set_by_pointer(st_errors, rd_fs_errors, (collected_number)stats_array[31]);
+            rrddim_set_by_pointer(st_errors, rd_flushing_errors, (collected_number)stats_array[34]);
             rrdset_done(st_errors);
         }
 

database/engine/pagecache.c

@@ -214,7 +214,7 @@ static void pg_cache_release_pages(struct rrdengine_instance *ctx, unsigned numb
  * This function returns the maximum number of pages allowed in the page cache.
  * The caller must hold the page cache lock.
  */
-static inline unsigned long pg_cache_hard_limit(struct rrdengine_instance *ctx)
+unsigned long pg_cache_hard_limit(struct rrdengine_instance *ctx)
 {
     /* it's twice the number of producers since we pin 2 pages per producer */
     return ctx->max_cache_pages + 2 * (unsigned long)ctx->stats.metric_API_producers;
@@ -225,7 +225,7 @@ static inline unsigned long pg_cache_hard_limit(struct rrdengine_instance *ctx)
  * number of pages below that number.
  * The caller must hold the page cache lock.
  */
-static inline unsigned long pg_cache_soft_limit(struct rrdengine_instance *ctx)
+unsigned long pg_cache_soft_limit(struct rrdengine_instance *ctx)
 {
     /* it's twice the number of producers since we pin 2 pages per producer */
     return ctx->cache_pages_low_watermark + 2 * (unsigned long)ctx->stats.metric_API_producers;
@@ -1029,14 +1029,14 @@ static void init_replaceQ(struct rrdengine_instance *ctx)
     assert(0 == uv_rwlock_init(&pg_cache->replaceQ.lock));
 }
 
-static void init_commited_page_index(struct rrdengine_instance *ctx)
+static void init_committed_page_index(struct rrdengine_instance *ctx)
 {
     struct page_cache *pg_cache = &ctx->pg_cache;
 
-    pg_cache->commited_page_index.JudyL_array = (Pvoid_t) NULL;
-    assert(0 == uv_rwlock_init(&pg_cache->commited_page_index.lock));
-    pg_cache->commited_page_index.latest_corr_id = 0;
-    pg_cache->commited_page_index.nr_commited_pages = 0;
+    pg_cache->committed_page_index.JudyL_array = (Pvoid_t) NULL;
+    assert(0 == uv_rwlock_init(&pg_cache->committed_page_index.lock));
+    pg_cache->committed_page_index.latest_corr_id = 0;
+    pg_cache->committed_page_index.nr_committed_pages = 0;
 }
 
 void init_page_cache(struct rrdengine_instance *ctx)
@@ -1049,7 +1049,7 @@ void init_page_cache(struct rrdengine_instance *ctx)
 
     init_metrics_index(ctx);
     init_replaceQ(ctx);
-    init_commited_page_index(ctx);
+    init_committed_page_index(ctx);
 }
 
 void free_page_cache(struct rrdengine_instance *ctx)
@@ -1062,9 +1062,9 @@ void free_page_cache(struct rrdengine_instance *ctx)
     struct rrdeng_page_descr *descr;
     struct page_cache_descr *pg_cache_descr;
 
-    /* Free commited page index */
-    ret_Judy = JudyLFreeArray(&pg_cache->commited_page_index.JudyL_array, PJE0);
-    assert(NULL == pg_cache->commited_page_index.JudyL_array);
+    /* Free committed page index */
+    ret_Judy = JudyLFreeArray(&pg_cache->committed_page_index.JudyL_array, PJE0);
+    assert(NULL == pg_cache->committed_page_index.JudyL_array);
     bytes_freed += ret_Judy;
 
     for (page_index = pg_cache->metrics_index.last_page_index ;

database/engine/pagecache.h

@@ -110,7 +110,7 @@ struct pg_cache_metrics_index {
 };
 
 /* gathers dirty pages to be written on disk */
-struct pg_cache_commited_page_index {
+struct pg_cache_committed_page_index {
     uv_rwlock_t lock;
 
     Pvoid_t JudyL_array;
@@ -122,7 +122,7 @@ struct pg_cache_commited_page_index {
      */
     Word_t latest_corr_id;
 
-    unsigned nr_commited_pages;
+    unsigned nr_committed_pages;
 };
 
 /*
@@ -140,7 +140,7 @@ struct page_cache { /* TODO: add statistics */
     uv_rwlock_t pg_cache_rwlock; /* page cache lock */
 
     struct pg_cache_metrics_index metrics_index;
-    struct pg_cache_commited_page_index commited_page_index;
+    struct pg_cache_committed_page_index committed_page_index;
     struct pg_cache_replaceQ replaceQ;
 
     unsigned page_descriptors;
@@ -182,6 +182,8 @@ extern void init_page_cache(struct rrdengine_instance *ctx);
 extern void free_page_cache(struct rrdengine_instance *ctx);
 extern void pg_cache_add_new_metric_time(struct pg_cache_page_index *page_index, struct rrdeng_page_descr *descr);
 extern void pg_cache_update_metric_times(struct pg_cache_page_index *page_index);
+extern unsigned long pg_cache_hard_limit(struct rrdengine_instance *ctx);
+extern unsigned long pg_cache_soft_limit(struct rrdengine_instance *ctx);
 
 static inline void
     pg_cache_atomic_get_pg_info(struct rrdeng_page_descr *descr, usec_t *end_timep, uint32_t *page_lengthp)

database/engine/rrdengine.c

@@ -5,9 +5,8 @@
 
 rrdeng_stats_t global_io_errors = 0;
 rrdeng_stats_t global_fs_errors = 0;
-rrdeng_stats_t global_pg_cache_warnings = 0;
-rrdeng_stats_t global_pg_cache_errors = 0;
 rrdeng_stats_t rrdeng_reserved_file_descriptors = 0;
+rrdeng_stats_t global_flushing_errors = 0;
 
 void sanity_check(void)
 {
@@ -253,6 +252,7 @@ void flush_pages_cb(uv_fs_t* req)
 {
     struct rrdengine_worker_config* wc = req->loop->data;
     struct rrdengine_instance *ctx = wc->ctx;
+    struct page_cache *pg_cache = &ctx->pg_cache;
     struct extent_io_descriptor *xt_io_descr;
     struct rrdeng_page_descr *descr;
     struct page_cache_descr *pg_cache_descr;
@@ -290,6 +290,10 @@ void flush_pages_cb(uv_fs_t* req)
     uv_fs_req_cleanup(req);
     free(xt_io_descr->buf);
     freez(xt_io_descr);
+
+    uv_rwlock_wrlock(&pg_cache->committed_page_index.lock);
+    pg_cache->committed_page_index.nr_committed_pages -= count;
+    uv_rwlock_wrunlock(&pg_cache->committed_page_index.lock);
 }
 
 /*
@@ -323,14 +327,14 @@ static int do_flush_pages(struct rrdengine_worker_config* wc, int force, struct
     if (force) {
         debug(D_RRDENGINE, "Asynchronous flushing of extent has been forced by page pressure.");
     }
-    uv_rwlock_wrlock(&pg_cache->commited_page_index.lock);
+    uv_rwlock_wrlock(&pg_cache->committed_page_index.lock);
     for (Index = 0, count = 0, uncompressed_payload_length = 0,
-         PValue = JudyLFirst(pg_cache->commited_page_index.JudyL_array, &Index, PJE0),
+         PValue = JudyLFirst(pg_cache->committed_page_index.JudyL_array, &Index, PJE0),
          descr = unlikely(NULL == PValue) ? NULL : *PValue ;
 
          descr != NULL && count != MAX_PAGES_PER_EXTENT ;
 
-         PValue = JudyLNext(pg_cache->commited_page_index.JudyL_array, &Index, PJE0),
+         PValue = JudyLNext(pg_cache->committed_page_index.JudyL_array, &Index, PJE0),
          descr = unlikely(NULL == PValue) ? NULL : *PValue) {
         uint8_t page_write_pending;
 
@@ -350,12 +354,11 @@ static int do_flush_pages(struct rrdengine_worker_config* wc, int force, struct
         rrdeng_page_descr_mutex_unlock(ctx, descr);
 
         if (page_write_pending) {
-            ret = JudyLDel(&pg_cache->commited_page_index.JudyL_array, Index, PJE0);
+            ret = JudyLDel(&pg_cache->committed_page_index.JudyL_array, Index, PJE0);
             assert(1 == ret);
-            --pg_cache->commited_page_index.nr_commited_pages;
         }
     }
-    uv_rwlock_wrunlock(&pg_cache->commited_page_index.lock);
+    uv_rwlock_wrunlock(&pg_cache->committed_page_index.lock);
 
     if (!count) {
         debug(D_RRDENGINE, "%s: no pages eligible for flushing.", __func__);
@@ -648,6 +651,9 @@ void async_cb(uv_async_t *handle)
     debug(D_RRDENGINE, "%s called, active=%d.", __func__, uv_is_active((uv_handle_t *)handle));
 }
 
+/* Flushes dirty pages when timer expires */
+#define TIMER_PERIOD_MS (1000)
+
 void timer_cb(uv_timer_t* handle)
 {
     struct rrdengine_worker_config* wc = handle->data;
@@ -657,12 +663,31 @@ void timer_cb(uv_timer_t* handle)
     rrdeng_test_quota(wc);
     debug(D_RRDENGINE, "%s: timeout reached.", __func__);
     if (likely(!wc->now_deleting.data)) {
-        unsigned total_bytes, bytes_written;
-
         /* There is free space so we can write to disk */
+        struct rrdengine_instance *ctx = wc->ctx;
+        struct page_cache *pg_cache = &ctx->pg_cache;
+        unsigned long total_bytes, bytes_written, nr_committed_pages, bytes_to_write = 0, producers, low_watermark,
+                      high_watermark;
+
+        uv_rwlock_wrlock(&pg_cache->committed_page_index.lock);
+        nr_committed_pages = pg_cache->committed_page_index.nr_committed_pages;
+        uv_rwlock_wrunlock(&pg_cache->committed_page_index.lock);
+        producers = ctx->stats.metric_API_producers;
+        /* are flushable pages more than 25% of the maximum page cache size */
+        high_watermark = (ctx->max_cache_pages * 25LLU) / 100;
+        low_watermark = (ctx->max_cache_pages * 5LLU) / 100; /* 5%, must be smaller than high_watermark */
+
+        if (nr_committed_pages > producers &&
+            /* committed to be written pages are more than the produced number */
+            nr_committed_pages - producers > high_watermark) {
+            /* Flushing speed must increase to stop page cache from filling with dirty pages */
+            bytes_to_write = (nr_committed_pages - producers - low_watermark) * RRDENG_BLOCK_SIZE;
+        }
+        bytes_to_write = MAX(DATAFILE_IDEAL_IO_SIZE, bytes_to_write);
+
         debug(D_RRDENGINE, "Flushing pages to disk.");
         for (total_bytes = bytes_written = do_flush_pages(wc, 0, NULL) ;
-             bytes_written && (total_bytes < DATAFILE_IDEAL_IO_SIZE) ;
+             bytes_written && (total_bytes < bytes_to_write) ;
              total_bytes += bytes_written) {
             bytes_written = do_flush_pages(wc, 0, NULL);
         }
@@ -675,9 +700,6 @@ void timer_cb(uv_timer_t* handle)
 #endif
 }
 
-/* Flushes dirty pages when timer expires */
-#define TIMER_PERIOD_MS (1000)
-
 #define MAX_CMD_BATCH_SIZE (256)
 
 void rrdeng_worker(void* arg)
@@ -771,8 +793,8 @@ void rrdeng_worker(void* arg)
                 /* First I/O should be enough to call completion */
                 bytes_written = do_flush_pages(wc, 1, cmd.completion);
                 if (bytes_written) {
-                    while (do_flush_pages(wc, 1, NULL)) {
-                        ; /* Force flushing of all commited pages. */
+                    while (do_flush_pages(wc, 1, NULL) && likely(!wc->now_deleting.data)) {
+                        ; /* Force flushing of all committed pages if there is free space. */
                     }
                 }
                 break;
@@ -789,7 +811,7 @@ void rrdeng_worker(void* arg)
     }
     info("Shutting down RRD engine event loop.");
     while (do_flush_pages(wc, 1, NULL)) {
-        ; /* Force flushing of all commited pages. */
+        ; /* Force flushing of all committed pages. */
     }
     wal_flush_transaction_buffer(wc);
     uv_run(loop, UV_RUN_DEFAULT);

database/engine/rrdengine.h

@@ -148,6 +148,7 @@ struct rrdengine_statistics {
     rrdeng_stats_t page_cache_descriptors;
     rrdeng_stats_t io_errors;
     rrdeng_stats_t fs_errors;
+    rrdeng_stats_t flushing_errors;
 };
 
 /* I/O errors global counter */
@@ -156,6 +157,8 @@ extern rrdeng_stats_t global_io_errors;
 extern rrdeng_stats_t global_fs_errors;
 /* number of File-Descriptors that have been reserved by dbengine */
 extern rrdeng_stats_t rrdeng_reserved_file_descriptors;
+/* inability to flush global counter */
+extern rrdeng_stats_t global_flushing_errors;
 
 struct rrdengine_instance {
     struct rrdengine_worker_config worker_config;

database/engine/rrdengineapi.c

@@ -173,9 +173,9 @@ void rrdeng_store_metric_next(RRDDIM *rd, usec_t point_in_time, storage_number n
 
         handle->descr = descr;
 
-        uv_rwlock_wrlock(&pg_cache->commited_page_index.lock);
-        handle->page_correlation_id = pg_cache->commited_page_index.latest_corr_id++;
-        uv_rwlock_wrunlock(&pg_cache->commited_page_index.lock);
+        uv_rwlock_wrlock(&pg_cache->committed_page_index.lock);
+        handle->page_correlation_id = pg_cache->committed_page_index.latest_corr_id++;
+        uv_rwlock_wrunlock(&pg_cache->committed_page_index.lock);
 
         if (0 == rd->rrdset->rrddim_page_alignment) {
             /* this is the leading dimension that defines chart alignment */
@@ -614,18 +614,31 @@ void rrdeng_commit_page(struct rrdengine_instance *ctx, struct rrdeng_page_descr
 {
     struct page_cache *pg_cache = &ctx->pg_cache;
     Pvoid_t *PValue;
+    unsigned nr_committed_pages;
 
     if (unlikely(NULL == descr)) {
-        debug(D_RRDENGINE, "%s: page descriptor is NULL, page has already been force-commited.", __func__);
+        debug(D_RRDENGINE, "%s: page descriptor is NULL, page has already been force-committed.", __func__);
         return;
     }
     assert(descr->page_length);
 
-    uv_rwlock_wrlock(&pg_cache->commited_page_index.lock);
-    PValue = JudyLIns(&pg_cache->commited_page_index.JudyL_array, page_correlation_id, PJE0);
+    uv_rwlock_wrlock(&pg_cache->committed_page_index.lock);
+    PValue = JudyLIns(&pg_cache->committed_page_index.JudyL_array, page_correlation_id, PJE0);
     *PValue = descr;
-    ++pg_cache->commited_page_index.nr_commited_pages;
-    uv_rwlock_wrunlock(&pg_cache->commited_page_index.lock);
+    nr_committed_pages = ++pg_cache->committed_page_index.nr_committed_pages;
+    uv_rwlock_wrunlock(&pg_cache->committed_page_index.lock);
+
+    if (nr_committed_pages >= (pg_cache_hard_limit(ctx) - (unsigned long)ctx->stats.metric_API_producers) / 2) {
+        /* 50% of pages have not been committed yet */
+        if (0 == (unsigned long)ctx->stats.flushing_errors) {
+            /* only print the first time */
+            error("Failed to flush quickly enough in dbengine instance \"%s\""
+                  ". Metric data will not be stored in the database"
+                  ", please reduce disk load or use a faster disk.", ctx->dbfiles_path);
+        }
+        rrd_stat_atomic_add(&ctx->stats.flushing_errors, 1);
+        rrd_stat_atomic_add(&global_flushing_errors, 1);
+    }
 
     pg_cache_put(ctx, descr);
 }
@@ -674,15 +687,15 @@ void *rrdeng_get_page(struct rrdengine_instance *ctx, uuid_t *id, usec_t point_i
  * You must not change the indices of the statistics or user code will break.
  * You must not exceed RRDENG_NR_STATS or it will crash.
  */
-void rrdeng_get_33_statistics(struct rrdengine_instance *ctx, unsigned long long *array)
+void rrdeng_get_35_statistics(struct rrdengine_instance *ctx, unsigned long long *array)
 {
     struct page_cache *pg_cache = &ctx->pg_cache;
 
     array[0] = (uint64_t)ctx->stats.metric_API_producers;
     array[1] = (uint64_t)ctx->stats.metric_API_consumers;
     array[2] = (uint64_t)pg_cache->page_descriptors;
     array[3] = (uint64_t)pg_cache->populated_pages;
-    array[4] = (uint64_t)pg_cache->commited_page_index.nr_commited_pages;
+    array[4] = (uint64_t)pg_cache->committed_page_index.nr_committed_pages;
     array[5] = (uint64_t)ctx->stats.pg_cache_insertions;
     array[6] = (uint64_t)ctx->stats.pg_cache_deletions;
     array[7] = (uint64_t)ctx->stats.pg_cache_hits;
@@ -711,7 +724,9 @@ void rrdeng_get_33_statistics(struct rrdengine_instance *ctx, unsigned long long
     array[30] = (uint64_t)global_io_errors;
     array[31] = (uint64_t)global_fs_errors;
     array[32] = (uint64_t)rrdeng_reserved_file_descriptors;
-    assert(RRDENG_NR_STATS == 33);
+    array[33] = (uint64_t)ctx->stats.flushing_errors;
+    array[34] = (uint64_t)global_flushing_errors;
+    assert(RRDENG_NR_STATS == 35);
 }
 
 /* Releases reference to page */

database/engine/rrdengineapi.h

@@ -8,7 +8,7 @@
 #define RRDENG_MIN_PAGE_CACHE_SIZE_MB (8)
 #define RRDENG_MIN_DISK_SPACE_MB (256)
 
-#define RRDENG_NR_STATS (33)
+#define RRDENG_NR_STATS (35)
 
 #define RRDENG_FD_BUDGET_PER_INSTANCE (50)
 
@@ -41,7 +41,7 @@ extern int rrdeng_load_metric_is_finished(struct rrddim_query_handle *rrdimm_han
 extern void rrdeng_load_metric_finalize(struct rrddim_query_handle *rrdimm_handle);
 extern time_t rrdeng_metric_latest_time(RRDDIM *rd);
 extern time_t rrdeng_metric_oldest_time(RRDDIM *rd);
-extern void rrdeng_get_33_statistics(struct rrdengine_instance *ctx, unsigned long long *array);
+extern void rrdeng_get_35_statistics(struct rrdengine_instance *ctx, unsigned long long *array);
 
 /* must call once before using anything */
 extern int rrdeng_init(struct rrdengine_instance **ctxp, char *dbfiles_path, unsigned page_cache_mb,