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Release: 2.6.2 Previous Releases
Publish Date: July, 2008 |
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Cluster Statistics Definitions |
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The following categories of cluster information and statistics are available for viewing and recording in the Terracotta Administrator Console.
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l1 = Terracotta client
l2 = Terracotta server
See the Glossary for definitions of commonly used terms. |
cache objects evict request
The total number of objects marked for eviction from the l1, or from the l2 to disk. Evicted objects are still referenced, and can be faulted back to the l1 from the l2 or from disk to l2. The SVT graphs this metric for each l1 and l2 separately. High counts imply that memory may be running low.
cache objects evicted
The number of objects actually evicted. If this metric is not close in value to cache objects evict request, then memory may not be getting freed quickly enough.
l1 l2 flush
The object flush rate when the l1 flushes objects to the l2 to free up memory or as a result of GC activity.
l2 faults from disk
The number of times the l2 has to load objects from disk to serve l1 object demand. A high faulting rate may indicate an overburdened l2.
l2 l1 fault
The number of times an l2 has to send objects to an l1 because the objects do not exist in the l1 local heap due to memory constraints. Better scalability is achieved when this number is lowered through improved locality and usage of an optimal number of JVMs.
memory (usage)
The amount of memory (heap) usage over time.
vm garbage collector
The standard Java garbage collector's behavior, tracked on all JVMs in the cluster.
distributed gc (distributed garbage collection, or DGC)
The behavior of the Terracotta tool that collects distributed garbage on an l2. The DGC can pause all other work on the l2 to ensure that no referenced objects are flagged for garbage collection.
l2 pending transactions
The number of transactions held in memory by an l2 while it optimizes these transactions before writing their changes to disk. Any object that is part of a pending transaction cannot be changed until the transaction is complete.
stage queue depth
The depth to which visibility into l2 work-queues is available. A larger depth value allows more detail to emerge on pending task-completion processes, bottlenecks due to application requests or behavior, types of work being done, and load conditions. Rising counts (of items in these processing queues) indicate backlogs and may point to performance degradation.
server transaction sequencer stats
Statistics on the l2 transaction sequencer, which sequences transactions as resources become available while maintaining transaction order.
network activity
The amount of data transmitted and received by the l2 in bytes per second.
l2 changes per broadcast
The number of updates to objects per broadcast message.
message monitor
The network message count flowing over TCP from Terracotta clients to the Terracotta server.
l2 broadcast count
The number of times that an l2 has transmitted changes to objects. This "broadcast" occurs any time the changed object is resident in more than one l1. This is not a true broadcast since messages are sent only to clients where the changed objects are resident.
l2 transaction count
The number of times an application goes into a synchronized mode — with boundaries defined by a Java lock — to read or write changes to objects. The transaction may contain any number of reads and writes. Once the lock is released and the transaction ends, changes are flushed.
l2 broadcast per transaction
The ratio of broadcasts to transactions. A high radio (close to 1) means that each broadcast is reporting few transactions, and implies an inefficient environment (high co-residency of objects).
system properties
Snapshot of all Java properties passed in and set at startup for each JVM. Used to determine configuration states at the time of data capture, and for comparison of configuration across JVMs.
thread dump
Displays a marker on all statistics graphs in the SVT at the point when a thread dump was taken using the Cluster statistics recorder. Clicking the marker displays the thread dump.
disk activity
The number of operations (reads and writes) per second, and the number of bytes per second (throughput). The number of reads corresponds to l2 faulting objects from disk, while writes corresponds to l2 flushing objects to disk. The SVT graphs the two aspects separately.
cpu (usage)
The percent of CPU resources being used. Dual-core processors are broken out into CPU0 and CPU1.
