ndbinfo: The NDB Cluster Information Database Number of requests that had to wait for pages to become available in buffer Number of requests that had to be read from pages on disk (pages were unavailable in buffer) You can use this table with NDB Cluster Disk Data tables to determine whether  DiskPageBufferMemory is sufficiently large to allow data to be read from the buffer rather from disk; minimizing disk seeks can help improve performance of such tables. You can determine the proportion of reads from  DiskPageBufferMemory  to the total number of reads using a query such as this one, which obtains this ratio as a percentage: The result from this query should be similar to what is shown here, with one row for each data node in the cluster (in this example, the cluster has 4 data nodes): hit_ratio  values approaching 100% indicate that only a very small number of reads are being made from disk rather than from the buffer, which means that Disk Data read performance is approaching an optimum level. If any of these values are less than 95%, this is a strong indicator that the setting for DiskPageBufferMemory  needs to be increased in the  config.ini  file. A change in  DiskPageBufferMemory  requires a rolling restart of all of the cluster’s data nodes before it takes effect. block_instance  refers to an instance of a kernel block. Together with the block name, this number can be used to look up a given instance in the  threadblocks  table. Using this information, you can obtain information about disk page buffer metrics relating to individual threads; an example query using  LIMIT 1 to limit the output to a single thread is shown here: mysql>  SELECT > node_id, thr_no, block_name, thread_name, pages_written, > pages_written_lcp, pages_read, log_waits, > page_requests_direct_return, page_requests_wait_queue, > page_requests_wait_io >  FROM ndbinfo.diskpagebuffer > INNER JOIN ndbinfo.threadblocks USING (node_id, block_instance) > INNER JOIN ndbinfo.threads USING (node_id, thr_no) >  WHERE block_name = ’PGMAN’ LIMIT 1\G *************************** 1. row *************************** Note SELECT node_id, 100 * page_requests_direct_return / (page_requests_direct_return + page_requests_wait_io) AS hit_ratio FROM ndbinfo.diskpagebuffer; Notes 4552 • page_requests_wait_io 4 rows in set (0.00 sec) +---------+-----------+ | node_id | hit_ratio | +---------+-----------+ | 5 | 97.6744 | | 6 | 97.6879 | | 7 | 98.1776 | | 8 | 98.1343 | +---------+-----------+