Getting btree statistics (number of nodes, max/min depth, etc) is useful for debugging and performance analysis.
The ability to consult them via non-public URIs is useful for view-engine and storage-engine engineers.
Example, when querying the per design doc specific debug URL:
$ curl -s 'http://localhost:9500/_set_view/default/_design/test3/_btree_stats' | python -mjson.tool
{
"id_btree":
{
"avg_elements_per_kp_node": 19.93181818181818,
"avg_elements_per_kv_node": 75.00750075007501,
"avg_kp_node_size": 3170.159090909091,
"avg_kp_node_size_compressed": 454.0511363636364,
"avg_kv_node_size": 2101.2100210021,
"avg_kv_node_size_compressed": 884.929492949295,
"btree_size": 3058201,
"chunk_threshold": 5120,
"file_size": 11866307,
"fragmentation": 74.22786213098988,
"kp_nodes": 176,
"kv_count": 250000,
"kv_nodes": 3333,
"max_depth": 4,
"max_elements_per_kp_node": 27,
"max_elements_per_kv_node": 100,
"max_kp_node_size": 4294,
"max_kp_node_size_compressed": 619,
"max_kv_node_size": 2801,
"max_kv_node_size_compressed": 1161,
"max_reduction_size": 133,
"min_depth": 4,
"min_elements_per_kp_node": 8,
"min_elements_per_kv_node": 75,
"min_kp_node_size": 1273,
"min_kp_node_size_compressed": 206,
"min_kv_node_size": 2101,
"min_kv_node_size_compressed": 849,
"min_reduction_size": 133
}
,
"view1":
{
"avg_elements_per_kp_node": 17.96416938110749,
"avg_elements_per_kv_node": 23.99923202457521,
"avg_kp_node_size": 3127.825732899023,
"avg_kp_node_size_compressed": 498.3436482084691,
"avg_kv_node_size": 3024.903235096477,
"avg_kv_node_size_compressed": 805.7447441681866,
"btree_size": 8789820,
"chunk_threshold": 5120,
"file_size": 11866307,
"fragmentation": 25.92623804524862,
"kp_nodes": 614,
"kv_count": 250000,
"kv_nodes": 10417,
"max_depth": 5,
"max_elements_per_kp_node": 21,
"max_elements_per_kv_node": 24,
"max_kp_node_size": 3676,
"max_kp_node_size_compressed": 606,
"max_kv_node_size": 3025,
"max_kv_node_size_compressed": 852,
"max_reduction_size": 141,
"min_depth": 5,
"min_elements_per_kp_node": 2,
"min_elements_per_kv_node": 16,
"min_kp_node_size": 357,
"min_kp_node_size_compressed": 108,
"min_kv_node_size": 2017,
"min_kv_node_size_compressed": 577,
"min_reduction_size": 137
}
}
$
Should be used with care, as it needs to traverse all the btrees to collect the statistics, which can take several minutes to several minutes, depending on the size of the trees.
Improvement
Major