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fix(csharp): prevent infinite polling in SEA metadata queries #347

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fix(csharp): prevent infinite polling in SEA metadata queries #347

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fix(csharp): add metadata timeout to ExecuteMetadataSqlAsync to preve…
msrathore-db Mar 13, 2026
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Merge branch 'main' into fix/sea-metadata-infinite-polling-timeout
msrathore-db Mar 13, 2026
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18 changes: 15 additions & 3 deletions csharp/src/StatementExecution/StatementExecutionConnection.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -734,16 +734,28 @@ async Task IGetObjectsDataProvider.PopulateColumnInfoAsync(string? catalogPatter

internal async Task<List<RecordBatch>> ExecuteMetadataSqlAsync(string sql, CancellationToken cancellationToken = default)
{
// Ensure metadata SQL always has a timeout to prevent infinite polling.
// The caller (e.g. GetObjects) may already supply a timeout token, but if
// the token is CancellationToken.None (e.g. when called from
// ExecuteMetadataCommandAsync → GetTablesAsync via ExecuteQuery()), the
// inner statement would have _queryTimeoutSeconds=0 and poll forever.
// Link the caller's token with a metadata timeout as a safety net.
using var metadataTimeoutCts = CreateMetadataTimeoutCts();
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@eric-wang-1990 eric-wang-1990 Mar 17, 2026

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It seems we have same bug for Thrift, can we fix that too?

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@msrathore-db msrathore-db Mar 20, 2026

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Good question! I investigated this and Thrift is not affected by this bug. Here's why:

  1. Thrift metadata calls use native RPC (e.g., TGetTablesReq) — a single request-response call, not SQL execution with polling.

  2. Databricks always returns DirectResults inline in the Thrift metadata response. The DatabricksConnection overrides GetResultSetMetadataAsync and GetRowSetAsync (DatabricksConnection.cs L923-927) to extract results directly from response.DirectResults! — never reaching PollForResponseAsync.

  3. The bug is SEA-specific because SEA metadata commands (e.g., SHOW TABLES) use ExecuteMetadataSqlAsync → StatementExecutionStatement → PollUntilCompleteAsync (a while(true) loop). When called with CancellationToken.None and _queryTimeoutSeconds=0, this loop runs forever. Thrift's path never enters this code.

The base HiveServer2Connection.PollForResponseAsync (L733) does have a polling loop, but it's only used by non-Databricks drivers (via HiveServer2ExtendedConnection) and for statement execution — not for Databricks metadata calls.

using var linkedCts = cancellationToken.CanBeCanceled
? CancellationTokenSource.CreateLinkedTokenSource(cancellationToken, metadataTimeoutCts.Token)
: null;
var effectiveToken = linkedCts?.Token ?? metadataTimeoutCts.Token;

var batches = new List<RecordBatch>();
using var stmt = (StatementExecutionStatement)CreateStatement();
stmt.SqlQuery = sql;
var result = await stmt.ExecuteQueryAsync(cancellationToken, isMetadataExecution: true).ConfigureAwait(false);
var result = await stmt.ExecuteQueryAsync(effectiveToken, isMetadataExecution: true).ConfigureAwait(false);
using var stream = result.Stream;
if (stream == null) return batches;
while (true)
{
cancellationToken.ThrowIfCancellationRequested();
var batch = await stream.ReadNextRecordBatchAsync(cancellationToken).ConfigureAwait(false);
effectiveToken.ThrowIfCancellationRequested();
var batch = await stream.ReadNextRecordBatchAsync(effectiveToken).ConfigureAwait(false);
if (batch == null) break;
batches.Add(batch);
}
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