Update 1.query-performance-metrics.md (vesoft-inc#2521)

docs-2.0-en/6.monitor-and-metrics/1.query-performance-metrics.md

@@ -9,7 +9,7 @@ Each metric of NebulaGraph consists of three fields: name, type, and time range.
 |Field|Example|Description|
 |-|-|-|
 |Metric name|`num_queries`|Indicates the function of the metric.|
-|Metric type|`sum`|Indicates how the metrics are collected. Supported types are SUM, AVG, RATE, and the P-th sample quantiles such as P75, P95, P99, and P99.9.|
+|Metric type|`sum`|Indicates how the metrics are collected. Supported types are SUM, AVG, RATE, and the P-th sample quantiles such as P75, P95, P99, and P999.|
 |Time range|`600`|The time range in seconds for the metric collection. Supported values are 5, 60, 600, and 3600, representing the last 5 seconds, 1 minute, 10 minutes, and 1 hour.|