Allow User to Specify Max Connections to DB (#37748)

<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
#### Description
Added additional field `MaxOpenConn` which allow users to specify the
maximum number of connections to DB server.

<!-- Issue number (e.g. #1234) or full URL to issue, if applicable. -->
#### Link to tracking issue
Fixes: #36752 

<!--Describe what testing was performed and which tests were added.-->
#### Testing
`TestMysqlIntegrationMetrics`

---------

Signed-off-by: Alok Kumar Singh <[email protected]>
Co-authored-by: Antoine Toulme <[email protected]>

Author: akstron

.chloggen/sql-receiver-connection-pool.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: 'enhancement'
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: 'sqlqueryreceiver'
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: "Allow users to specify the maximum number of concurrent open connections to DB server using `max_open_conn` config parameter"
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [36752]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

receiver/sqlqueryreceiver/README.md

@@ -40,6 +40,7 @@ The configuration supports the following top-level fields:
 - `telemetry` (optional) Defines settings for the component's own telemetry - logs, metrics or traces.
   - `telemetry.logs` (optional) Defines settings for the component's own logs.
     - `telemetry.logs.query` (optional, default `false`) If set to `true`, every time a SQL query is run, the text of the query and the values of its parameters will be logged together with the debug log `"Running query"`.
+- `max_open_conn` (optional, default `0`): The maximumn number of open connections to the sql server. <= 0 means unlimited
 
 [storage_extension]: https://github.com/open-telemetry/opentelemetry-collector-contrib/tree/main/extension/storage/filestorage
 

receiver/sqlqueryreceiver/config.go

@@ -14,6 +14,8 @@ import (
 
 type Config struct {
 	sqlquery.Config `mapstructure:",squash"`
+	// The maximumn number of open connections to the sql server. <= 0 means unlimited
+	MaxOpenConn int `mapstructure:"max_open_conn"`
 }
 
 func createDefaultConfig() component.Config {

receiver/sqlqueryreceiver/integration_test.go

@@ -713,6 +713,7 @@ func TestMysqlIntegrationMetrics(t *testing.T) {
 				rCfg := cfg.(*Config)
 				rCfg.Driver = MySQL.Driver
 				rCfg.DataSource = MySQL.ConnectionString(ci.Host(t), nat.Port(ci.MappedPort(t, MySQL.Port)))
+				rCfg.MaxOpenConn = 5
 				rCfg.Queries = []sqlquery.Query{
 					{
 						SQL: "select genre, count(*), avg(imdb_rating) from movie group by genre order by genre desc",

receiver/sqlqueryreceiver/receiver.go

@@ -45,7 +45,15 @@ func createMetricsReceiverFunc(sqlOpenerFunc sqlquery.SQLOpenerFunc, clientProvi
 			}
 			id := component.MustNewIDWithName("sqlqueryreceiver", fmt.Sprintf("query-%d: %s", i, query.SQL))
 			dbProviderFunc := func() (*sql.DB, error) {
-				return sqlOpenerFunc(sqlCfg.Driver, sqlCfg.DataSource)
+				dbPool, err := sqlOpenerFunc(sqlCfg.Driver, sqlCfg.DataSource)
+				if err != nil {
+					return nil, err
+				}
+
+				if dbPool != nil {
+					dbPool.SetMaxOpenConns(sqlCfg.MaxOpenConn)
+				}
+				return dbPool, nil
 			}
 			scope := pcommon.NewInstrumentationScope()
 			scope.SetName(metadata.ScopeName)