接入 OpenTelemetry 1.17.0，覆盖 HTTP、HttpClient、.NET Runtime 和数据库链路。

新增 EF Core 数据库拦截器，记录耗时、失败数、慢查询数、TraceId、查询标签和 SQL 哈希；默认不记录完整 SQL及参数。
未配置 OTLP Collector 时不启动 SDK，避免无收益的性能开销。
为课表的作息、课程、灵活课程、考试、实验等六类查询增加稳定标签。
增加可配置的 500ms 慢查询阈值，以及生产环境变量示例。
README 补充 MySQL 慢查询与 EXPLAIN ANALYZE 操作规范。

.env.example

@@ -36,6 +36,16 @@ Cache__AnalyticsExpirationMinutes=3
 Cache__AnalyticsLocalExpirationSeconds=30
 Cache__MaximumPayloadKilobytes=2048
 
+# OpenTelemetry 默认收集 HTTP、运行时和数据库指标；配置 OTLP 地址后才会外发。
+Observability__Enabled=true
+Observability__ServiceName=jiaowu-api
+Observability__SlowQueryThresholdMilliseconds=500
+# 默认不记录完整 SQL，避免日志或追踪系统接触业务数据。
+Observability__IncludeSqlText=false
+Observability__MaximumSqlTextLength=2000
+# OTEL_EXPORTER_OTLP_ENDPOINT=https://otel-collector.example.edu.cn:4317
+# OTEL_EXPORTER_OTLP_HEADERS=Authorization=Bearer%20REPLACE_WITH_TOKEN
+
 # 运维控制台备份目录必须位于持久化、仅服务账号可写的位置。
 Operations__BackupDirectory=/var/lib/jiaowu/backups
 Operations__BackupWarningHours=24

README.md

@@ -322,6 +322,34 @@ Redis 只作为可丢弃的查询缓存。连接失败时应用回源数据库
 `allkeys-lfu` 淘汰策略，不启用持久化。`compose.app.example.yml` 不创建 Redis；
 如需连接外部 Redis，在 `.env` 中配置上述连接串即可。
 
+### OpenTelemetry 与慢查询定位
+
+应用已接入 OpenTelemetry 的 ASP.NET Core、HttpClient、.NET Runtime 指标，并通过
+`Jiaowu.Api.Database` ActivitySource 和 Meter 记录 EF Core 数据库命令。配置
+`OTEL_EXPORTER_OTLP_ENDPOINT` 后才启动 OpenTelemetry SDK 并向 OTLP Collector 外发；
+未配置时不会创建无处消费的请求 Span，也不会尝试连接本地 Collector，结构化慢查询日志
+仍然有效。
+
+```text
+Observability__Enabled=true
+Observability__ServiceName=jiaowu-api
+Observability__SlowQueryThresholdMilliseconds=500
+OTEL_EXPORTER_OTLP_ENDPOINT=https://otel-collector.example.edu.cn:4317
+```
+
+数据库指标包括 `jiaowu.db.command.duration`、`jiaowu.db.command.slow` 和
+`jiaowu.db.command.failed`。为关键 EF 查询添加 `TagWith("模块.查询名")` 后，日志和
+追踪会直接显示该稳定名称；无标签查询只显示操作类型和 SQL 模板哈希。默认
+`Observability__IncludeSqlText=false`，不会把 SQL、参数值或连接串发送到日志和追踪
+系统。仅在受控诊断窗口内临时启用完整 SQL 模板，并限制 Collector 权限与保留时间。
+
+应用侧阈值用于关联接口、TraceId 和查询名称；生产 MySQL 还应由数据库管理员启用慢查询
+日志，并将 `long_query_time` 设为与应用阈值一致。先按查询哈希/标签汇总高频慢查询，再
+对脱敏后的 `SELECT` 在测试库或只读副本执行 `EXPLAIN ANALYZE`，根据实际扫描行数和循环
+次数决定是否补组合索引或改写投影。`EXPLAIN ANALYZE` 会真实执行语句，不能直接用于生产
+写操作。参考 [MySQL 慢查询日志](https://dev.mysql.com/doc/refman/8.0/en/slow-query-log.html)
+和 [MySQL 8.4 EXPLAIN](https://dev.mysql.com/doc/refman/8.4/en/explain.html)。
+
 ### 后台任务与 RabbitMQ
 
 自动排课、课表发布和补考自动生成使用数据库 Outbox 保存任务消息。创建业务任务与

src/Jiaowu.Api/Infrastructure/Observability/DatabaseCommandTelemetryInterceptor.cs

@@ -0,0 +1,281 @@
+using System.Data.Common;
+using System.Diagnostics;
+using System.Diagnostics.Metrics;
+using System.Security.Cryptography;
+using System.Text;
+using Microsoft.EntityFrameworkCore.Diagnostics;
+
+namespace Jiaowu.Api.Infrastructure.Observability;
+
+public sealed class DatabaseCommandTelemetryInterceptor(
+    ObservabilityOptions options,
+    ILogger<DatabaseCommandTelemetryInterceptor> logger)
+    : DbCommandInterceptor
+{
+    public const string ActivitySourceName = "Jiaowu.Api.Database";
+    public const string MeterName = "Jiaowu.Api.Database";
+
+    private static readonly ActivitySource ActivitySource =
+        new(ActivitySourceName);
+    private static readonly Meter Meter = new(MeterName);
+    private static readonly Histogram<double> CommandDuration =
+        Meter.CreateHistogram<double>(
+            "jiaowu.db.command.duration",
+            "ms",
+            "EF Core database command duration");
+    private static readonly Counter<long> SlowCommandCount =
+        Meter.CreateCounter<long>(
+            "jiaowu.db.command.slow",
+            "{command}",
+            "EF Core commands exceeding the configured slow-query threshold");
+    private static readonly Counter<long> FailedCommandCount =
+        Meter.CreateCounter<long>(
+            "jiaowu.db.command.failed",
+            "{command}",
+            "Failed EF Core database commands");
+
+    public override DbDataReader ReaderExecuted(
+        DbCommand command,
+        CommandExecutedEventData eventData,
+        DbDataReader result)
+    {
+        Observe(command, eventData.Duration, "reader");
+        return result;
+    }
+
+    public override ValueTask<DbDataReader> ReaderExecutedAsync(
+        DbCommand command,
+        CommandExecutedEventData eventData,
+        DbDataReader result,
+        CancellationToken cancellationToken = default)
+    {
+        Observe(command, eventData.Duration, "reader");
+        return ValueTask.FromResult(result);
+    }
+
+    public override int NonQueryExecuted(
+        DbCommand command,
+        CommandExecutedEventData eventData,
+        int result)
+    {
+        Observe(command, eventData.Duration, "nonquery");
+        return result;
+    }
+
+    public override ValueTask<int> NonQueryExecutedAsync(
+        DbCommand command,
+        CommandExecutedEventData eventData,
+        int result,
+        CancellationToken cancellationToken = default)
+    {
+        Observe(command, eventData.Duration, "nonquery");
+        return ValueTask.FromResult(result);
+    }
+
+    public override object? ScalarExecuted(
+        DbCommand command,
+        CommandExecutedEventData eventData,
+        object? result)
+    {
+        Observe(command, eventData.Duration, "scalar");
+        return result;
+    }
+
+    public override ValueTask<object?> ScalarExecutedAsync(
+        DbCommand command,
+        CommandExecutedEventData eventData,
+        object? result,
+        CancellationToken cancellationToken = default)
+    {
+        Observe(command, eventData.Duration, "scalar");
+        return ValueTask.FromResult(result);
+    }
+
+    public override void CommandFailed(
+        DbCommand command,
+        CommandErrorEventData eventData) =>
+        Observe(
+            command,
+            eventData.Duration,
+            "failed",
+            eventData.Exception.GetType().Name);
+
+    public override Task CommandFailedAsync(
+        DbCommand command,
+        CommandErrorEventData eventData,
+        CancellationToken cancellationToken = default)
+    {
+        Observe(
+            command,
+            eventData.Duration,
+            "failed",
+            eventData.Exception.GetType().Name);
+        return Task.CompletedTask;
+    }
+
+    public override void CommandCanceled(
+        DbCommand command,
+        CommandEndEventData eventData) =>
+        Observe(command, eventData.Duration, "canceled", "canceled");
+
+    public override Task CommandCanceledAsync(
+        DbCommand command,
+        CommandEndEventData eventData,
+        CancellationToken cancellationToken = default)
+    {
+        Observe(command, eventData.Duration, "canceled", "canceled");
+        return Task.CompletedTask;
+    }
+
+    private void Observe(
+        DbCommand command,
+        TimeSpan duration,
+        string commandKind,
+        string? errorType = null)
+    {
+        if (!options.Enabled) return;
+
+        var queryName = GetQueryName(command.CommandText);
+        var statementHash = GetStatementHash(command.CommandText);
+        var provider = GetProviderName(command);
+        var traceId = Activity.Current?.TraceId.ToString() ?? "none";
+        var tags = new TagList
+        {
+            { "db.system.name", provider },
+            { "db.operation.name", commandKind },
+            { "db.query.name", queryName }
+        };
+        if (errorType is not null)
+            tags.Add("error.type", errorType);
+
+        var durationMilliseconds = duration.TotalMilliseconds;
+        CommandDuration.Record(durationMilliseconds, tags);
+        if (errorType is not null)
+            FailedCommandCount.Add(1, tags);
+
+        using var activity = ActivitySource.StartActivity(
+            ActivityKind.Client,
+            Activity.Current?.Context ?? default,
+            startTime: DateTimeOffset.UtcNow - duration,
+            name: queryName);
+        if (activity is not null)
+        {
+            activity.SetTag("db.system.name", provider);
+            activity.SetTag("db.operation.name", commandKind);
+            activity.SetTag("db.query.name", queryName);
+            activity.SetTag("db.statement.hash", statementHash);
+            activity.SetTag(
+                "db.namespace",
+                EmptyToNull(command.Connection?.Database));
+            if (options.IncludeSqlText)
+            {
+                activity.SetTag(
+                    "db.query.text",
+                    Truncate(command.CommandText, options.MaximumSqlTextLength));
+            }
+            if (errorType is not null)
+            {
+                activity.SetTag("error.type", errorType);
+                activity.SetStatus(ActivityStatusCode.Error, errorType);
+            }
+            activity.SetEndTime(DateTime.UtcNow);
+        }
+
+        if (errorType is not null)
+        {
+            logger.LogError(
+                "Database command failed after {DurationMs:F1} ms: " +
+                "{QueryName} ({CommandKind}, {Provider}, hash {StatementHash}, " +
+                "error {ErrorType}, trace {TraceId}).",
+                durationMilliseconds,
+                queryName,
+                commandKind,
+                provider,
+                statementHash,
+                errorType,
+                traceId);
+            return;
+        }
+
+        if (durationMilliseconds < options.SlowQueryThresholdMilliseconds)
+            return;
+
+        SlowCommandCount.Add(1, tags);
+        if (options.IncludeSqlText)
+        {
+            logger.LogWarning(
+                "Slow database command took {DurationMs:F1} ms: " +
+                "{QueryName} ({CommandKind}, {Provider}, hash {StatementHash}, " +
+                "trace {TraceId}). " +
+                "SQL template: {SqlTemplate}",
+                durationMilliseconds,
+                queryName,
+                commandKind,
+                provider,
+                statementHash,
+                traceId,
+                Truncate(command.CommandText, options.MaximumSqlTextLength));
+        }
+        else
+        {
+            logger.LogWarning(
+                "Slow database command took {DurationMs:F1} ms: " +
+                "{QueryName} ({CommandKind}, {Provider}, hash {StatementHash}, " +
+                "trace {TraceId}).",
+                durationMilliseconds,
+                queryName,
+                commandKind,
+                provider,
+                statementHash,
+                traceId);
+        }
+    }
+
+    internal static string GetQueryName(string commandText)
+    {
+        using var reader = new StringReader(commandText);
+        while (reader.ReadLine() is { } line)
+        {
+            var trimmed = line.Trim();
+            if (trimmed.Length == 0) continue;
+            if (trimmed.StartsWith("-- ", StringComparison.Ordinal))
+                return Truncate(trimmed[3..].Trim(), 120);
+            return $"{FirstToken(trimmed)}:{GetStatementHash(commandText)}";
+        }
+
+        return $"unknown:{GetStatementHash(commandText)}";
+    }
+
+    internal static string GetStatementHash(string commandText)
+    {
+        var bytes = SHA256.HashData(Encoding.UTF8.GetBytes(commandText));
+        return Convert.ToHexString(bytes.AsSpan(0, 6)).ToLowerInvariant();
+    }
+
+    private static string FirstToken(string value)
+    {
+        var end = value.IndexOfAny([' ', '\t', '\r', '\n', '(']);
+        var token = end < 0 ? value : value[..end];
+        return token.Length == 0
+            ? "command"
+            : token.ToLowerInvariant();
+    }
+
+    private static string GetProviderName(DbCommand command)
+    {
+        var typeName = command.GetType().FullName ?? command.GetType().Name;
+        if (typeName.Contains("MySql", StringComparison.OrdinalIgnoreCase))
+            return "mysql";
+        if (typeName.Contains("Sqlite", StringComparison.OrdinalIgnoreCase))
+            return "sqlite";
+        return "other_sql";
+    }
+
+    private static string? EmptyToNull(string? value) =>
+        string.IsNullOrWhiteSpace(value) ? null : value;
+
+    private static string Truncate(string value, int maximumLength) =>
+        value.Length <= maximumLength
+            ? value
+            : value[..maximumLength];
+}