Don't emit INFO spans for administrative queries

This prevents internal queries like
`SELECT @@max_allowed_packet` from showing up in user
tracing unless tracing level TRACE is allowed.

src/conn/mod.rs

@@ -887,7 +887,7 @@ impl Conn {
     /// Do nothing if socket address is already in [`Opts`] or if `prefer_socket` is `false`.
     async fn read_socket(&mut self) -> Result<()> {
         if self.inner.opts.prefer_socket() && self.inner.socket.is_none() {
-            let row_opt = self.query_first("SELECT @@socket").await?;
+            let row_opt = self.query_internal("SELECT @@socket").await?;
             self.inner.socket = row_opt.unwrap_or((None,)).0;
         }
         Ok(())
@@ -898,7 +898,7 @@ impl Conn {
         let max_allowed_packet = if let Some(value) = self.opts().max_allowed_packet() {
             Some(value)
         } else {
-            self.query_first("SELECT @@max_allowed_packet").await?
+            self.query_internal("SELECT @@max_allowed_packet").await?
         };
         if let Some(stream) = self.inner.stream.as_mut() {
             stream.set_max_allowed_packet(max_allowed_packet.unwrap_or(DEFAULT_MAX_ALLOWED_PACKET));
@@ -911,7 +911,7 @@ impl Conn {
         let wait_timeout = if let Some(value) = self.opts().wait_timeout() {
             Some(value)
         } else {
-            self.query_first("SELECT @@wait_timeout").await?
+            self.query_internal("SELECT @@wait_timeout").await?
         };
         self.inner.wait_timeout = Duration::from_secs(wait_timeout.unwrap_or(28800) as u64);
         Ok(())

src/conn/routines/query.rs

@@ -2,7 +2,7 @@ use futures_core::future::BoxFuture;
 use futures_util::FutureExt;
 use mysql_common::constants::Command;
 #[cfg(feature = "tracing")]
-use tracing::{field, info_span, Instrument, Level};
+use tracing::{field, info_span, span_enabled, trace_span, Instrument, Level};
 
 use crate::{Conn, TextProtocol};
 
@@ -12,24 +12,35 @@ use super::Routine;
 #[derive(Debug, Copy, Clone)]
 pub struct QueryRoutine<'a> {
     data: &'a [u8],
+    #[cfg_attr(not(feature = "tracing"), allow(dead_code))]
+    internal: bool,
 }
 
 impl<'a> QueryRoutine<'a> {
-    pub fn new(data: &'a [u8]) -> Self {
-        Self { data }
+    pub fn new(data: &'a [u8], internal: bool) -> Self {
+        Self { data, internal }
     }
 }
 
 impl Routine<()> for QueryRoutine<'_> {
     fn call<'a>(&'a mut self, conn: &'a mut Conn) -> BoxFuture<'a, crate::Result<()>> {
         #[cfg(feature = "tracing")]
-        let span = info_span!(
-            "mysql_async::query",
-            mysql_async.connection.id = conn.id(),
-            mysql_async.query.sql = field::Empty
-        );
+        let span = if self.internal {
+            trace_span!(
+                "mysql_async::query",
+                mysql_async.connection.id = conn.id(),
+                mysql_async.query.sql = field::Empty
+            )
+        } else {
+            info_span!(
+                "mysql_async::query",
+                mysql_async.connection.id = conn.id(),
+                mysql_async.query.sql = field::Empty
+            )
+        };
+
         #[cfg(feature = "tracing")]
-        if tracing::span_enabled!(Level::DEBUG) {
+        if span_enabled!(Level::DEBUG) {
             // The statement may contain sensitive data. Restrict to DEBUG.
             span.record(
                 "mysql_async.query.sql",

src/queryable/mod.rs

@@ -106,9 +106,33 @@ impl Conn {
     where
         Q: AsQuery + 'a,
     {
-        self.routine(QueryRoutine::new(query.as_query().as_ref()))
+        self.routine(QueryRoutine::new(query.as_query().as_ref(), false))
             .await
     }
+
+    /// Used for internal querying of connection settings,
+    /// bypassing instrumentation meant for user queries.
+    // This is a merge of `Queryable::query_first` and `Conn::query_iter`.
+    // TODO: find a cleaner way without duplicating code.
+    pub(crate) fn query_internal<'a, T, Q>(&'a mut self, query: Q) -> BoxFuture<'a, Option<T>>
+    where
+        Q: AsQuery + 'a,
+        T: FromRow + Send + 'static,
+    {
+        async move {
+            self.routine(QueryRoutine::new(query.as_query().as_ref(), true))
+                .await?;
+            let mut result: QueryResult<'a, 'static, TextProtocol> = QueryResult::new(self);
+            let output = if result.is_empty() {
+                None
+            } else {
+                result.next().await?.map(crate::from_row)
+            };
+            result.drop_result().await?;
+            Ok(output)
+        }
+        .boxed()
+    }
 }
 
 /// Methods of this trait are used to execute database queries.
@@ -456,7 +480,7 @@ impl Queryable for Conn {
         Q: AsQuery + 'a,
     {
         async move {
-            self.routine(QueryRoutine::new(query.as_query().as_ref()))
+            self.routine(QueryRoutine::new(query.as_query().as_ref(), false))
                 .await?;
             Ok(QueryResult::new(self))
         }