Performance metrics computation methodology (#4041)

book/src/SUMMARY.md

@@ -20,6 +20,7 @@
   - [Ledger Replication](ledger-replication.md)
   - [Secure Vote Signing](vote-signing.md)
   - [Staking Delegation and Rewards](stake-delegation-and-rewards.md)
+  - [Performance Metrics](performance-metrics.md)
 
 - [Anatomy of a Fullnode](fullnode.md)
   - [TPU](tpu.md)

book/src/performance-metrics.md

@@ -0,0 +1,29 @@
+# Performance Metrics
+
+Solana cluster performance is measured as average number of transactions per second
+that the network can sustain (TPS). And, how long it takes for a transaction to be
+confirmed by super majority of the cluster (Confirmation Time).
+
+Each cluster node maintains various counters that are incremented on certain events.
+These counters are periodically uploaded to a cloud based database. Solana's metrics
+dashboard fetches these counters, and computes the performance metrics and displays
+it on the dashboard. 
+
+## TPS
+
+The leader node's banking stage maintains a count of transactions that it processed.
+The dashboard displays the count averaged over 2 second period in the TPS time series
+graph. The dashboard also shows per second mean, maximum and total TPS as a running
+counter.
+
+## Confirmation Time
+
+Each validator node maintains a list of active ledger forks that are visible to the node.
+A fork is considered to be frozen when the node has received and processed all entries
+corresponding to the fork. A fork is considered to be confirmed when it receives cumulative
+super majority vote, and when one of its children forks is frozen.
+
+The node assigns a timestamp to every new fork, and computes the time it took to confirm
+the fork. This time is reflected as validator confirmation time in performance metrics.
+The performance dashboard displays the average of each validator node's confirmation time
+as a time series graph.