Detect deadlock in dbengine page cache (#6911)

* Detect deadlock in dbengine page cache when there are too many metrics and print error message

* Resolve dbengine deadlock by dropping metrics when page cache is too small and define relevant alarms

* Changed printing deadlock errors to only happen once per dbengine instance

1 files changed, 13 insertions, 0 deletions

diff --git a/database/engine/rrdengine.h b/database/engine/rrdengine.h
index 6f6a6f8ffd..6447a685bd 100644
--- a/database/engine/rrdengine.h
+++ b/database/engine/rrdengine.h
@@ -148,12 +148,25 @@ struct rrdengine_statistics {
     rrdeng_stats_t page_cache_descriptors;
     rrdeng_stats_t io_errors;
     rrdeng_stats_t fs_errors;
+    rrdeng_stats_t pg_cache_warnings;
+    rrdeng_stats_t pg_cache_errors;
 };
 
 /* I/O errors global counter */
 extern rrdeng_stats_t global_io_errors;
 /* File-System errors global counter */
 extern rrdeng_stats_t global_fs_errors;
+/*
+ * Page cache warnings global counter.
+ * Some page cache instance is near critical utilization where metrics will fail to be stored.
+ */
+extern rrdeng_stats_t global_pg_cache_warnings;
+/*
+ * Page cache errors global counter.
+ * Some page cache instance has hit critical utilization where metrics failed to be stored as a deadlock resolution
+ * measure.
+ */
+extern rrdeng_stats_t global_pg_cache_errors;
 /* number of File-Descriptors that have been reserved by dbengine */
 extern rrdeng_stats_t rrdeng_reserved_file_descriptors;