[skywalking] 01/01: Polish doc to mention Top N sampling mechanism.

[wu...@apache.org]

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wusheng pushed a commit to branch polish-doc
in repository https://gitbox.apache.org/repos/asf/skywalking.git

commit 2430bef837003cd722e063e80f8746c6762222d8
Author: Wu Sheng <wu...@foxmail.com>
AuthorDate: Wed Nov 23 16:53:35 2022 +0800

    Polish doc to mention Top N sampling mechanism.
---
 docs/en/concepts-and-designs/lal.md             | 4 ++++
 docs/en/setup/backend/slow-cache-command.md     | 4 +++-
 docs/en/setup/backend/slow-db-statement.md      | 5 ++++-
 docs/en/setup/service-agent/virtual-cache.md    | 2 ++
 docs/en/setup/service-agent/virtual-database.md | 2 ++
 5 files changed, 15 insertions(+), 2 deletions(-)

diff --git a/docs/en/concepts-and-designs/lal.md b/docs/en/concepts-and-designs/lal.md
index 48e978abbe..f81d96f125 100644
--- a/docs/en/concepts-and-designs/lal.md
+++ b/docs/en/concepts-and-designs/lal.md
@@ -280,6 +280,10 @@ metrics:
 `slowSql` aims to convert LogData to DatabaseSlowStatement. It extracts data from `parsed` result and save them as DatabaseSlowStatement. SlowSql will not abort or edit logs, you can use other LAL for further processing.
 SlowSql will reuse `service`, `layer` and `timestamp` of extractor, so it is necessary to use `SlowSQL` after setting these.
 We require a log tag `"LOG_KIND" = "SLOW_SQL"` to make OAP distinguish slow SQL logs from other log reports.
+
+**Note**, slow SQL sampling would only flag this SQL in the candidate list. The OAP server would run statistic per service
+and only persistent the top 50 every 10(controlled by `topNReportPeriod: ${SW_CORE_TOPN_REPORT_PERIOD:10}`) minutes by default.  
+
 An example of JSON sent to OAP is as following:
 ``` json
 [
diff --git a/docs/en/setup/backend/slow-cache-command.md b/docs/en/setup/backend/slow-cache-command.md
index dfad3bdb62..29f8e252d2 100644
--- a/docs/en/setup/backend/slow-cache-command.md
+++ b/docs/en/setup/backend/slow-cache-command.md
@@ -10,4 +10,6 @@ Here's the format of the settings (in milliseconds):
 The default settings are `default:20,redis:10`. `Reserved Cache type` is **default**, which is the default threshold for all
 cache types, unless set explicitly.
 
-**Note**: The threshold should not be set too small, like `1ms`. Although it works in theory, OAP performance issues may arise if your system statement access time is usually more than 1ms.
+**Note**: 
+1. The threshold should not be set too small, like `1ms`. Although it works in theory, OAP performance issues may arise if your system statement access time is usually more than 1ms.
+2. The OAP server would run statistic per service and only persistent the top 50 every 10(controlled by `topNReportPeriod: ${SW_CORE_TOPN_REPORT_PERIOD:10}`) minutes by default.
\ No newline at end of file
diff --git a/docs/en/setup/backend/slow-db-statement.md b/docs/en/setup/backend/slow-db-statement.md
index 4a4a914644..240fe935c6 100644
--- a/docs/en/setup/backend/slow-db-statement.md
+++ b/docs/en/setup/backend/slow-db-statement.md
@@ -10,4 +10,7 @@ Here's the format of the settings (in milliseconds):
 The default settings are `default:200,mongodb:100`. `Reserved DB type` is **default**, which is the default threshold for all
 database types, unless set explicitly.
 
-**Note**: The threshold should not be set too small, like `1ms`. Although it works in theory, OAP performance issues may arise if your system statement access time is usually more than 1ms.
+**Note**: 
+1. The threshold should not be set too small, like `1ms`. Although it works in theory, OAP performance issues may arise if your system statement access time is usually more than 1ms.
+2. The OAP server would run statistic per service and only persistent the top 50 every 10(controlled by `topNReportPeriod: ${SW_CORE_TOPN_REPORT_PERIOD:10}`) minutes by default.
+
diff --git a/docs/en/setup/service-agent/virtual-cache.md b/docs/en/setup/service-agent/virtual-cache.md
index 7c56572926..b159b7ee80 100644
--- a/docs/en/setup/service-agent/virtual-cache.md
+++ b/docs/en/setup/service-agent/virtual-cache.md
@@ -14,3 +14,5 @@ The cache operation span should have
 - Tag key = `cache.cmd`, value = the cache command , e.g. get,set,del
 - Tag key = `cache.key`, value = the cache key
 - If the cache system is in-memory (e.g. Guava-cache), agents' plugin would create a local span usually, and the span's peer would be null ,otherwise the peer is the network address(IP or domain) of Cache server.
+
+Ref [slow cache doc](../backend/slow-cache-command.md) to know more slow Cache commands settings. 
\ No newline at end of file
diff --git a/docs/en/setup/service-agent/virtual-database.md b/docs/en/setup/service-agent/virtual-database.md
index 7acb158eff..88c09577a9 100644
--- a/docs/en/setup/service-agent/virtual-database.md
+++ b/docs/en/setup/service-agent/virtual-database.md
@@ -12,3 +12,5 @@ The Database access span should have
 - Tag key = `db.statement`, value = SQL statement
 - Tag key = `db.type`, value = the type of Database
 - Span's peer is the network address(IP or domain) of Database server.
+
+Ref [slow cache doc](../backend/slow-db-statement.md) to know more slow SQL settings.