dbengine extent cache (#10293)

* Add initial extent cache implementation

* Integrate extent cache with dbengine.

1 files changed, 24 insertions, 0 deletions

diff --git a/database/engine/rrdengine.h b/database/engine/rrdengine.h
index eb13d8474e..87af04bff9 100644
--- a/database/engine/rrdengine.h
+++ b/database/engine/rrdengine.h
@@ -88,6 +88,7 @@ struct extent_io_descriptor {
     int release_descr;
     struct rrdeng_page_descr *descr_array[MAX_PAGES_PER_EXTENT];
     Word_t descr_commit_idx_array[MAX_PAGES_PER_EXTENT];
+    struct extent_io_descriptor *next; /* multiple requests to be served by the same cached extent */
 };
 
 struct generic_io_descriptor {
@@ -99,6 +100,27 @@ struct generic_io_descriptor {
     struct completion *completion;
 };
 
+struct extent_cache_element {
+    struct extent_info *extent; /* The ABA problem is avoided with the help of fileno below */
+    unsigned fileno;
+    struct extent_cache_element *prev; /* LRU */
+    struct extent_cache_element *next; /* LRU */
+    struct extent_io_descriptor *inflight_io_descr; /* I/O descriptor for in-flight extent */
+    uint8_t pages[MAX_PAGES_PER_EXTENT * RRDENG_BLOCK_SIZE];
+};
+
+#define MAX_CACHED_EXTENTS 16 /* cannot be over 32 to fit in 32-bit architectures */
+
+/* Initialize by setting the structure to zero */
+struct extent_cache {
+    struct extent_cache_element extent_array[MAX_CACHED_EXTENTS];
+    unsigned allocation_bitmap; /* 1 if the corresponding position in the extent_array is allocated */
+    unsigned inflight_bitmap; /* 1 if the corresponding position in the extent_array is waiting for I/O */
+
+    struct extent_cache_element *replaceQ_head; /* LRU */
+    struct extent_cache_element *replaceQ_tail; /* MRU */
+};
+
 struct rrdengine_worker_config {
     struct rrdengine_instance *ctx;
 
@@ -122,6 +144,8 @@ struct rrdengine_worker_config {
     volatile unsigned queue_size;
     struct rrdeng_cmdqueue cmd_queue;
 
+    struct extent_cache xt_cache;
+
     int error;
 };