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Fix sequential buffered seek #5440

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merged 6 commits into from
Nov 28, 2023
+46 −15
Merged

Fix sequential buffered seek #5440

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0b235bc
Increment directly after column length read
NinoFloris Nov 22, 2023
4bd78b7
And do so in the other cases as well
NinoFloris Nov 22, 2023
95bc46a
Only skip on positive non-zero column lengths
NinoFloris Nov 22, 2023
b623fd7
Change ConsumeRowSequential as well
NinoFloris Nov 22, 2023
efab93f
Remove recoverability code
NinoFloris Nov 25, 2023
8c457a4
Add test
NinoFloris Nov 28, 2023
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45 changes: 30 additions & 15 deletions src/Npgsql/NpgsqlDataReader.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1921,10 +1921,13 @@ int SeekToColumnNonSequential(int ordinal, DataFormat dataFormat, bool resumable
Debug.Assert(ordinal != currentColumn);
if (ordinal > currentColumn)
{
for (; currentColumn < ordinal - 1; currentColumn++)
// Written as a while to be able to increment _column directly after reading into it.
while (_column < ordinal - 1)
{
columnLength = buffer.ReadInt32();
if (columnLength is not -1)
_column++;
Debug.Assert(columnLength >= -1);
if (columnLength > 0)
buffer.Skip(columnLength);
}
columnLength = buffer.ReadInt32();
Expand Down Expand Up @@ -1962,7 +1965,7 @@ int SeekBackwards()
for (var lastColumnRead = _columns.Count; ordinal >= lastColumnRead; lastColumnRead++)
{
(Buffer.ReadPosition, var lastLen) = _columns[lastColumnRead - 1];
if (lastLen is not -1)
if (lastLen > 0)
buffer.Skip(lastLen);
var len = Buffer.ReadInt32();
_columns.Add((Buffer.ReadPosition, len));
Expand Down Expand Up @@ -2026,17 +2029,21 @@ async ValueTask<int> Core(bool async, bool commit, int ordinal, DataFormat dataF
}

// Seek to the requested column
int columnLength;
var buffer = Buffer;
for (; _column < ordinal - 1; _column++)
// Written as a while to be able to increment _column directly after reading into it.
while (_column < ordinal - 1)
{
await buffer.Ensure(4, async).ConfigureAwait(false);
var len = buffer.ReadInt32();
if (len != -1)
await buffer.Skip(len, async).ConfigureAwait(false);
columnLength = buffer.ReadInt32();
_column++;
Debug.Assert(columnLength >= -1);
if (columnLength > 0)
await buffer.Skip(columnLength, async).ConfigureAwait(false);
}

await buffer.Ensure(4, async).ConfigureAwait(false);
var columnLength = buffer.ReadInt32();
columnLength = buffer.ReadInt32();
_column = ordinal;

PgReader.Init(columnLength, dataFormat, resumableOp);
Expand All @@ -2054,11 +2061,14 @@ bool TrySeekBuffered(int ordinal, out int columnLength)
// Skip over unwanted fields
columnLength = -1;
var buffer = Buffer;
for (; _column < ordinal - 1; _column++)
// Written as a while to be able to increment _column directly after reading into it.
while (_column < ordinal - 1)
{
if (buffer.ReadBytesLeft < 4)
return false;
columnLength = buffer.ReadInt32();
_column++;
Debug.Assert(columnLength >= -1);
if (columnLength > 0)
{
if (buffer.ReadBytesLeft < columnLength)
Expand All @@ -2085,7 +2095,7 @@ bool TrySeekBuffered(int ordinal, out int columnLength)

Task ConsumeRow(bool async)
{
Debug.Assert(State == ReaderState.InResult || State == ReaderState.BeforeResult);
Debug.Assert(State is ReaderState.InResult or ReaderState.BeforeResult);

if (!_canConsumeRowNonSequentially)
return ConsumeRowSequential(async);
Expand All @@ -2100,13 +2110,18 @@ async Task ConsumeRowSequential(bool async)
await PgReader.CommitAsync(resuming: false).ConfigureAwait(false);
else
PgReader.Commit(resuming: false);

// Skip over the remaining columns in the row
for (; _column < ColumnCount - 1; _column++)
var buffer = Buffer;
// Written as a while to be able to increment _column directly after reading into it.
while (_column < ColumnCount - 1)
{
await Buffer.Ensure(4, async).ConfigureAwait(false);
var len = Buffer.ReadInt32();
if (len != -1)
await Buffer.Skip(len, async).ConfigureAwait(false);
await buffer.Ensure(4, async).ConfigureAwait(false);
var columnLength = buffer.ReadInt32();
_column++;
Debug.Assert(columnLength >= -1);
if (columnLength > 0)
await buffer.Skip(columnLength, async).ConfigureAwait(false);
}
}
}
Expand Down