c# - 在 ANTs 分析器信息的帮助下识别性能瓶颈

Question

这段代码运行的很慢:

public static class DB
    {
        readonly static InlineSql sql = new InlineSql();

        public static IEnumerable<LabItem> GetLabItemsFromLabLineItems(IEnumerable<LabLineItem> items)
        {
            /*
             * Business Rule : 
             * The sproc used to retrieve lab line items has no way of "grouping" lab items out of line items.
             * To compensate, the sproc orders its results by IDCode, we group everything and use the first of each grouping to represent that ID Code.
             * That very same item is also the first item in its Items property.
             * */
            return items
                .GroupBy(c => c.IDCode , c => c, (c, d) => d.First())
                .Select(c => new LabItem(c.IDCode, c.OrderGuid, c.Name, c.SignificantDtm, c.Status, c.Description, items.Where(d => string.Compare(d.IDCode, c.IDCode, true) == 0 )));
        }        
    }

特别是我们将 d.IDCode 与 c.IDCode 进行比较的选择语句似乎是问题所在。此行报告来自 ANTS 的命中数为 9000 万，%Time 为 14.8。 items.count大约 9 千。

我知道我的断点没有被击中 9000 万次。这里的命中数是什么意思？

其他有用的代码:

LabItem有List<LabLineItem>这就是我们在这里比较的。 LabLineItem.Equals :

    public override bool Equals(object obj)
    {
        LabLineItem otherItem = obj as LabLineItem;

        if (otherItem == null) return false;

        return
            OrderGuid == otherItem.OrderGuid
            && IDCode == otherItem.IDCode
            && SignificantDtm == otherItem.SignificantDtm
            && ObservationGuid == otherItem.ObservationGuid
            && string.Compare(Value, otherItem.Value, true) == 0;
    }
    public override int GetHashCode()
    {
        return
            OrderGuid.GetHashCode()
            ^ IDCode.GetHashCode()
            ^ SignificantDtm.GetHashCode()
            ^ ObservationGuid.GetHashCode();
    }

Answer 1

ANTS 表示调用 string.Compare 的 Select 被命中了 9000 万次，因为对于主列表中的每个项目，它都会再次搜索整个列表.

主要的 9000 次迭代中的每一次都会导致 9000 次额外的迭代，因此 string.Compare 必须至少调用 81,000,000 次。

我建议构建一个分组缓存，然后使用它来构建 LabItem。

也许是这样的:

var groupedItems = items.GroupBy(c => c.IDCode);

return items.Select(c => 
                new LabItem(c.IDCode, c.OrderGuid, c.Name, c.SignificantDtm, c.Status, c.Description, 
                groupedItems.Where(d => string.Compare(d.Key, c.IDCode, true) == 0 ).SelectMany(group => group)));