Thursday July 27, 2006

Understanding the cn=monitor entry

• backendMonitorDN -- This specifies the DNs of the monitor entries for each of the backends in the server. The backend monitor entries provide details about the server's interaction with the backend databases. The contents of these entries could easily constitute a separate post.
  
  
• bytesSent -- This specifies the total number of data bytes included in the responses that it has sent to clients. Note that this only includes data bytes and does not include packet headers (e.g., link-level, IP, and TCP headers).
  
  
• cache-avail-bytes -- This specifies the amount of free memory in the system that could possibly be using for caching. Note that it does *not* specify how much of the cache is unused like one might think. Honestly, it's not all that useful.
  
  
• connection -- This is a multivalued attribute with a separate line per established connection. This attribute will only appear if the monitor entry is retrieved by the root DN (e.g., "cn=Directory Manager"). Values are constructed in a colon-delimited form with the following components:
  
  1. The slot in the connection table, which generally equals the file descriptor number
  2. A timestamp that specifies when the connection was established (in UTC)
  3. The number of operations initiated on the connection
  4. The number of operations completed on the connection
  5. If the connection is in the process of reading data from the client, then the letter "r". Otherwise, it will be blank
  6. The DN of the authenticated user for the connection
  7. The protocol the client is using to communicate with the server
  
  
  
• connectionPeak -- This specifies the maximum number of concurrent connections that have been established to the server at any given time.
  
  
• currentConnections -- This specifies the number of connections that are currently established to the server.
  
  
• currentTime -- This specifies the current time according to the system clock on the server (in UTC).
  
  
• dTableSize -- This specifies the size of the file descriptor table for the server. This should be equal to the value of the nsslapd-maxdescriptors configuration attribute.
  
  
• entriesSent -- This specifies the total number of search result entries sent to clients in response to search requests.
  
  
• heapMaxHighHits -- This specifies the number of times that the server heap has grown large enough that it was necessary to free entries in the cache while holding an exclusive lock on the cache. Having this value increase is less desirable than having the heapMaxLowHits value increase, because it can have a significant impact on performance.
  
  
• heapMaxLowHits -- This specifies the number of times that the server heap has grown large enough that it was necessary to free entries in the cache, but without the need to lock the entire cache. This will have a lesser impact on performance than cases in which it is necessary to hold the lock while freeing entries.
  
  
• nBackends -- This specifies the number of backends (also called databases) configured in the server.
  
  
• opsCompleted -- This specifies the total number of operations that have completed processing since the server started. The difference between opsInitiated and opsCompleted should equal the number of operations in progress.
  
  
• opsInitiated -- This specifies the total number of operations that have been initiated since the server started.
  
  
• readWaiters -- This specifies the total number of client connections for which the Directory Server is waiting to read more data from the client (i.e., the client has started sending a request but has not yet completed it). This should be equal to the number of connections with the "r" notation in the connection attribute.
  
  
• request-que-backlog -- This specifies the number of requests that are currently sitting in the work queue waiting to be picked up by a worker thread. Having more than a couple of requests sitting in the work queue at any given time generally isn't a good thing because it means that all of the worker threads are busy processing other requests so new requests have to wait.
  
  
• startTime -- This specifies the time that the server was started (in UTC time).
  
  
• threads -- This specifies the number of worker threads currently configured for use in the server (as controlled by the nsslapd-threadnumber configuration attribute).
  
  
• version -- This is the Directory Server version string. It can be altered to an extent via the nsslapd-versionstring configuration attribute to help it deal with clients that foolishly are hard-coded to only work with a specific server version, but in general changing that string is not recommended.