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Optimize NpgsqlDataReader.NextResult async state machine #6638

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Merged
vonzshik merged 1 commit into from
Aug 28, 2026
+52 −45
Merged

Optimize NpgsqlDataReader.NextResult async state machine #6638

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97 changes: 52 additions & 45 deletions src/Npgsql/NpgsqlDataReader.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -472,50 +472,7 @@ async Task<bool> NextResult(bool async, bool isConsuming = false, CancellationTo

if ((Command.WrappingBatch is not null || StatementIndex is 0) && Command.InternalBatchCommands[StatementIndex] is { HasOutputParameters: true } command)
{
// If output parameters are present and this is the first row of the resultset,
// we must always read it in non-sequential mode because it will be traversed twice (once
// here for the parameters, then as a regular row).
msg = await Connector.ReadMessage(async, dataRowLoadingMode: DataRowLoadingMode.NonSequential).ConfigureAwait(false);
ProcessMessage(msg);
if (msg.Code == BackendMessageCode.DataRow)
{
Debug.Assert(RowDescription != null);
Debug.Assert(State == ReaderState.BeforeResult);

try
{
// Temporarily set our state to InResult and non-sequential to allow us to read the values, and in any order.
var isSequential = _isSequential;
var currentPosition = Buffer.ReadPosition;
State = ReaderState.InResult;
_isSequential = false;
try
{
command.PopulateOutputParameters(this, _commandLogger);

// On success we want to revert any row and column state for the user to be able to read the same row again.
if (async)
await PgReader.CommitAsync().ConfigureAwait(false);
else
PgReader.Commit();

State = ReaderState.BeforeResult; // Set the state back
Buffer.ReadPosition = currentPosition; // Restore position
_column = -1;
}
finally
{
// To be on the safe side we always revert this CommandBehavior state change, including on failure.
_isSequential = isSequential;
}
}
catch (Exception e)
{
// TODO: ideally we should flow down to global exception filter and consume there
await Consume(async, firstException: e).ConfigureAwait(false);
throw;
}
}
msg = await ReadMessageWithOutputParameters(async, command).ConfigureAwait(false);
}
else
{
Expand Down Expand Up @@ -647,6 +604,56 @@ async ValueTask ConsumeResultSet(bool async)
}
}

async ValueTask<IBackendMessage> ReadMessageWithOutputParameters(bool async, NpgsqlBatchCommand command)
{
// If output parameters are present and this is the first row of the resultset,
// we must always read it in non-sequential mode because it will be traversed twice (once
// here for the parameters, then as a regular row).
var msg = await Connector.ReadMessage(async, dataRowLoadingMode: DataRowLoadingMode.NonSequential).ConfigureAwait(false);
ProcessMessage(msg);
if (msg.Code == BackendMessageCode.DataRow)
{
Debug.Assert(RowDescription != null);
Debug.Assert(State == ReaderState.BeforeResult);

try
{
// Temporarily set our state to InResult and non-sequential to allow us to read the values, and in any order.
var isSequential = _isSequential;
var currentPosition = Buffer.ReadPosition;
State = ReaderState.InResult;
_isSequential = false;
try
{
command.PopulateOutputParameters(this, _commandLogger);

// On success we want to revert any row and column state for the user to be able to read the same row again.
if (async)
await PgReader.CommitAsync().ConfigureAwait(false);
else
PgReader.Commit();

State = ReaderState.BeforeResult; // Set the state back
Buffer.ReadPosition = currentPosition; // Restore position
_column = -1;
}
finally
{
// To be on the safe side we always revert this CommandBehavior state change, including on failure.
_isSequential = isSequential;
}
}
catch (Exception e)
{
// TODO: ideally we should flow down to global exception filter and consume there
await Consume(async, firstException: e).ConfigureAwait(false);
throw;
}
}

return msg;
}

/// <summary>
/// Note that in SchemaOnly mode there are no resultsets, and we read nothing from the backend (all
/// RowDescriptions have already been processed and are available)
Expand Down Expand Up @@ -971,7 +978,7 @@ public override int FieldCount
/// Consumes all result sets for this reader, leaving the connector ready for sending and processing further
/// queries
/// </summary>
async Task Consume(bool async, Exception? firstException = null)
async ValueTask Consume(bool async, Exception? firstException = null)
{
var exceptions = firstException is null ? null : new List<Exception> { firstException };

Expand Down
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