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Fix archive compaction OOM on large parquet groups #792

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Merged
erikdarlingdata merged 1 commit into from
Apr 6, 2026
Merged

Fix archive compaction OOM on large parquet groups #792

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95 changes: 72 additions & 23 deletions Lite/Services/ArchiveService.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -305,18 +305,8 @@ private void CompactParquetFiles()
}
}

/* Compact each group that has more than one file (or any non-monthly files) */
using var con = new DuckDBConnection("DataSource=:memory:");
con.Open();

/* Cap memory to avoid multi-GB spikes decompressing large parquet archives.
DuckDB will spill excess to its temp directory automatically. */
using (var pragma = con.CreateCommand())
{
pragma.CommandText = "SET memory_limit = '2GB'; SET preserve_insertion_order = false;";
pragma.ExecuteNonQuery();
}

/* Compact each group that has more than one file (or any non-monthly files).
Each group gets its own DuckDB connection so memory is fully released between groups. */
var totalMerged = 0;
var totalRemoved = 0;

Expand Down Expand Up @@ -346,16 +336,16 @@ DuckDB will spill excess to its temp directory automatically. */
var sourcePaths = files
.Select(f => Path.Combine(_archivePath, f).Replace("\\", "/"))
.ToList();
var pathList = string.Join(", ", sourcePaths.Select(p => $"'{p}'"));

/* Build SELECT with column exclusions for specific tables.
Only exclude columns that actually exist in the source files
(they may have been stripped in a previous compaction). */
/* Determine column exclusions up front using all source files */
var selectClause = "*";
if (CompactionExcludeColumns.TryGetValue(table, out var excludeCols))
{
using var schemaCmd = con.CreateCommand();
schemaCmd.CommandText = $"SELECT column_name FROM (DESCRIBE SELECT * FROM read_parquet([{pathList}], union_by_name=true))";
using var schemaCon = new DuckDBConnection("DataSource=:memory:");
schemaCon.Open();
var allPathList = string.Join(", ", sourcePaths.Select(p => $"'{p}'"));
using var schemaCmd = schemaCon.CreateCommand();
schemaCmd.CommandText = $"SELECT column_name FROM (DESCRIBE SELECT * FROM read_parquet([{allPathList}], union_by_name=true))";
using var reader = schemaCmd.ExecuteReader();
var existingCols = new HashSet<string>(StringComparer.OrdinalIgnoreCase);
while (reader.Read()) existingCols.Add(reader.GetString(0));
Expand All @@ -367,10 +357,65 @@ Only exclude columns that actually exist in the source files
}
}

using var cmd = con.CreateCommand();
cmd.CommandText = $"COPY (SELECT {selectClause} FROM read_parquet([{pathList}], union_by_name=true)) " +
$"TO '{tempPath}' (FORMAT PARQUET, COMPRESSION ZSTD, ROW_GROUP_SIZE 122880)";
cmd.ExecuteNonQuery();
if (sourcePaths.Count <= 2)
{
/* Small group — single-pass merge */
using var con = new DuckDBConnection("DataSource=:memory:");
con.Open();
using (var pragma = con.CreateCommand())
{
pragma.CommandText = "SET memory_limit = '4GB'; SET preserve_insertion_order = false;";
pragma.ExecuteNonQuery();
}

var pathList = string.Join(", ", sourcePaths.Select(p => $"'{p}'"));
using var cmd = con.CreateCommand();
cmd.CommandText = $"COPY (SELECT {selectClause} FROM read_parquet([{pathList}], union_by_name=true)) " +
$"TO '{tempPath}' (FORMAT PARQUET, COMPRESSION ZSTD, ROW_GROUP_SIZE 122880)";
cmd.ExecuteNonQuery();
}
else
{
/* Large group — incremental merge (pairs) to keep peak memory low.
Sort smallest-first so early merges are cheap. */
var sorted = sourcePaths
.OrderBy(p => new FileInfo(p.Replace("/", "\\")).Length)
.ToList();

var currentPath = sorted[0];
var intermediateFiles = new List<string>();

for (var i = 1; i < sorted.Count; i++)
{
var stepOutput = i < sorted.Count - 1
? targetPath + $".step{i}.tmp"
: tempPath;

using var con = new DuckDBConnection("DataSource=:memory:");
con.Open();
using (var pragma = con.CreateCommand())
{
pragma.CommandText = "SET memory_limit = '4GB'; SET preserve_insertion_order = false;";
pragma.ExecuteNonQuery();
}

var pairList = $"'{currentPath}', '{sorted[i]}'";
using var cmd = con.CreateCommand();
cmd.CommandText = $"COPY (SELECT {selectClause} FROM read_parquet([{pairList}], union_by_name=true)) " +
$"TO '{stepOutput}' (FORMAT PARQUET, COMPRESSION ZSTD, ROW_GROUP_SIZE 122880)";
cmd.ExecuteNonQuery();

/* Clean up previous intermediate file */
if (intermediateFiles.Count > 0)
{
var prev = intermediateFiles[^1];
try { File.Delete(prev); } catch { /* best effort */ }
}

intermediateFiles.Add(stepOutput);
currentPath = stepOutput;
}
}

/* Remove originals */
var removed = 0;
Expand Down Expand Up @@ -404,11 +449,15 @@ Only exclude columns that actually exist in the source files
{
_logger?.LogError(ex, "Failed to compact {Month}/{Table} ({Count} files)", month, table, files.Count);

/* Clean up temp file on failure */
/* Clean up temp and intermediate files on failure */
if (File.Exists(tempPath))
{
try { File.Delete(tempPath); } catch { /* best effort */ }
}
foreach (var stepFile in Directory.GetFiles(_archivePath, $"{targetMonth}_{table}.parquet.step*.tmp"))
{
try { File.Delete(stepFile); } catch { /* best effort */ }
}
}
}

Expand Down
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