How to improve this query performance in Linq?

Question

I have a large table and would like to know if it's possible to improve performance for queries.

allDocumentsWithPersianMonth has 25000000 record

    var normalDocuments = allDocumentsWithPersianMonth.Where(x => x.DocumentTypeId != 8 && x.DocumentTypeId != 9);
    var debitOpening = allDocumentsWithPersianMonth.Where(x => x.DocumentTypeId == 8);
    var creditOpening = allDocumentsWithPersianMonth.Where(x => x.DocumentTypeId == 8);
    var debitClosing = allDocumentsWithPersianMonth.Where(x => x.DocumentTypeId == 9);
    var creditClosing = allDocumentsWithPersianMonth.Where(x => x.DocumentTypeId == 9);

    return allDocumentsWithPersianMonth
        .GroupBy(x => new { x.DetailId, x.DetailCode, x.DetailDescription, x.PersianMonth })
        .Select(g => new AccountsAgingViewModel
        {
            DetailId = g.Key.DetailId,
            DetailCode = g.Key.DetailCode,
            DetailDescription = g.Key.DetailDescription,
            FarvardinDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 1).Sum(x => x.Debit),
            OrdibeheshtDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 2).Sum(x => x.Debit),
            KhordadDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 3).Sum(x => x.Debit),
            TirDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 4).Sum(x => x.Debit),
            MordadDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 5).Sum(x => x.Debit),
            ShahrivarDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 6).Sum(x => x.Debit),
            MehrDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 7).Sum(x => x.Debit),
            AbanDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 8).Sum(x => x.Debit),
            AzarDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 9).Sum(x => x.Debit),
            DeyDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 10).Sum(x => x.Debit),
            BahmanDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 11).Sum(x => x.Debit),
            EsfandDebit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 12).Sum(x => x.Debit),
            FarvardinCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 1).Sum(x => x.Credit),
            OrdibeheshtCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 2).Sum(x => x.Credit),
            KhordadCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 3).Sum(x => x.Credit),
            TirCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 4).Sum(x => x.Credit),
            MordadCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 5).Sum(x => x.Credit),
            ShahrivarCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 6).Sum(x => x.Credit),
            MehrCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 7).Sum(x => x.Credit),
            AbanCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 8).Sum(x => x.Credit),
            AzarCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 9).Sum(x => x.Credit),
            DeyCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 10).Sum(x => x.Credit),
            BahmanCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 11).Sum(x => x.Credit),
            EsfandCredit = normalDocuments.Where(x => x.DetailId == g.Key.DetailId && x.PersianMonth == 12).Sum(x => x.Credit),
            DebitSumOpening = debitOpening.Where(y => y.DetailId == g.Key.DetailId).Sum(x => x.Debit),
            DebitSumClosing = debitClosing.Where(y => y.DetailId == g.Key.DetailId).Sum(x => x.Credit),
            CreditSumOpening = creditOpening.Where(y => y.DetailId == g.Key.DetailId).Sum(x => x.Debit),
            CreditSumClosing = creditClosing.Where(y => y.DetailId == g.Key.DetailId).Sum(x => x.Credit),
        })

    .ToList();

Answer 1

You should first eliminate the execution of the same queries. For instance check the following approach. Instead of iterating through the normalDocuments each time for each month, we iterate just once and group the documents based on month. Then we create a dictionary with key the PersianMonth and value the corresponding sum of Debit.

Doing so we will go from 24 iterations to just 1. Then we define a func to get the value of debit or credit for a month from this dictionary. From your model a deposit might either a debit or a credit. So by passing the boolean parameted isDebit you would identify if you want to read the value of Debit or Credit.

This defintion may need some change, since I don't know the type of Debit and Credit and I just assumed that this is an decimal.

 .Select(g => 
 {
     var groupedDocuments = normalDocuments
                                .Where(x => x.DetailId == g.Key.DetailId)
                                .GroupBy(x => x.PersianMonth)
                                .ToDictionary(x => x.Key, 
                                              x => new DepositTypes(x.Sum(y=>y.Debit), x.Sum(y=>y.Credit));

     Func<int, bool, decimal> getValueFunc = (id, isDebit) 
         => groupedDocuments.TryGetValue(id, out var value) 
                ? (isDebit ? value.Debit ?? value.Credit) 
                : 0;

     return new AccountsAgingViewModel
     {
        DetailId = g.Key.DetailId,
        DetailCode = g.Key.DetailCode,
        DetailDescription = g.Key.DetailDescription,
        FarvardinDebit = getValueFunc(1, isDeposit: true);
        OrdibeheshtDebit = getValueFunc(2, isDeposit: true);
        // etc.
     };
}

private class DepositTypes
{
    public decimal Debit { get; }
    public decimal Credit {get; }

    public DepositTypes(decimal debit, decimal credit)
    {
        Debit = debit;
        Credit = credit;
    }
}

Answer 2

Some options to check:

1. Look at generated SQL query, maybe you just need to add some indexes (with help of execution plan).
2. Load all data to the memory in more specific structures (Dictionary, for example) and then select. Looks like you have a lot of queries to DB.