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fix: reduce memory usage in parquet checkpoint archiver

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Stream CheckpointFile trees directly to parquet rows instead of
materializing all rows in a giant intermediate slice. This eliminates
~1.9GB per host of redundant allocations (repeated string headers)
and removes the expensive sort on millions of 104-byte structs.

Key changes:
- Replace flattenCheckpointFile + sortParquetRows + WriteHostRows with
  streaming WriteCheckpointFile that walks the tree with sorted keys
- Reduce results channel buffer from len(hostEntries) to 2 for
  back-pressure (at most NumWorkers+2 results in flight)
- Workers send CheckpointFile trees instead of []ParquetMetricRow
- Write rows in small 1024-element batches via reusable buffer

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Entire-Checkpoint: f31dc1847539
This commit is contained in:
Jan Eitzinger
2026-03-18 17:32:16 +01:00
parent bb6915771d
commit 09501df3c2
3 changed files with 155 additions and 120 deletions
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176
pkg/metricstore/parquetArchive.go
View File

@@ -14,7 +14,6 @@ import (
"path/filepath"
"sort"
cclog "github.com/ClusterCockpit/cc-lib/v2/ccLogger"
pq "github.com/parquet-go/parquet-go"
)
@@ -32,37 +31,6 @@ type ParquetMetricRow struct {
Value float32 `parquet:"value"`
}
// flattenCheckpointFile recursively converts a CheckpointFile tree into Parquet rows.
// The scope path is built from the hierarchy: host level is "node", then child names
// map to scope/scope_id (e.g., "socket0" → scope="socket", scope_id="0").
func flattenCheckpointFile(cf *CheckpointFile, cluster, hostname, scope, scopeID string, rows []ParquetMetricRow) []ParquetMetricRow {
for metricName, cm := range cf.Metrics {
ts := cm.Start
for _, v := range cm.Data {
if !v.IsNaN() {
rows = append(rows, ParquetMetricRow{
Cluster: cluster,
Hostname: hostname,
Metric: metricName,
Scope: scope,
ScopeID: scopeID,
Timestamp: ts,
Frequency: cm.Frequency,
Value: float32(v),
})
}
ts += cm.Frequency
}
}
for childName, childCf := range cf.Children {
childScope, childScopeID := parseScopeFromName(childName)
rows = flattenCheckpointFile(childCf, cluster, hostname, childScope, childScopeID, rows)
}
return rows
}
// parseScopeFromName infers scope and scope_id from a child level name.
// Examples: "socket0" → ("socket", "0"), "core12" → ("core", "12"),
// "a0" (accelerator) → ("accelerator", "0").
@@ -93,15 +61,17 @@ func parseScopeFromName(name string) (string, string) {
}
// parquetArchiveWriter supports incremental writes to a Parquet file.
// Each call to WriteHostRows writes one row group (typically one host's data),
// avoiding accumulation of all rows in memory.
// Uses streaming writes to avoid accumulating all rows in memory.
type parquetArchiveWriter struct {
writer *pq.GenericWriter[ParquetMetricRow]
bw *bufio.Writer
f *os.File
batch []ParquetMetricRow // reusable batch buffer
count int
}
const parquetBatchSize = 1024
// newParquetArchiveWriter creates a streaming Parquet writer with Zstd compression.
func newParquetArchiveWriter(filename string) (*parquetArchiveWriter, error) {
if err := os.MkdirAll(filepath.Dir(filename), CheckpointDirPerms); err != nil {
@@ -119,31 +89,85 @@ func newParquetArchiveWriter(filename string) (*parquetArchiveWriter, error) {
pq.Compression(&pq.Zstd),
)
return &parquetArchiveWriter{writer: writer, bw: bw, f: f}, nil
return &parquetArchiveWriter{
writer: writer,
bw: bw,
f: f,
batch: make([]ParquetMetricRow, 0, parquetBatchSize),
}, nil
}
// WriteHostRows sorts rows by (metric, timestamp) in-place, writes them,
// and flushes to create a separate row group.
func (w *parquetArchiveWriter) WriteHostRows(rows []ParquetMetricRow) error {
sort.Slice(rows, func(i, j int) bool {
if rows[i].Metric != rows[j].Metric {
return rows[i].Metric < rows[j].Metric
}
return rows[i].Timestamp < rows[j].Timestamp
})
// WriteCheckpointFile streams a CheckpointFile tree directly to Parquet rows,
// writing metrics in sorted order without materializing all rows in memory.
// Produces one row group per call (typically one host's data).
func (w *parquetArchiveWriter) WriteCheckpointFile(cf *CheckpointFile, cluster, hostname, scope, scopeID string) error {
w.writeLevel(cf, cluster, hostname, scope, scopeID)
if _, err := w.writer.Write(rows); err != nil {
return fmt.Errorf("writing parquet rows: %w", err)
// Flush remaining batch
if len(w.batch) > 0 {
if _, err := w.writer.Write(w.batch); err != nil {
return fmt.Errorf("writing parquet rows: %w", err)
}
w.count += len(w.batch)
w.batch = w.batch[:0]
}
if err := w.writer.Flush(); err != nil {
return fmt.Errorf("flushing parquet row group: %w", err)
}
w.count += len(rows)
return nil
}
// writeLevel recursively writes metrics from a CheckpointFile level.
// Metric names and child names are sorted for deterministic, compression-friendly output.
func (w *parquetArchiveWriter) writeLevel(cf *CheckpointFile, cluster, hostname, scope, scopeID string) {
// Sort metric names for deterministic order
metricNames := make([]string, 0, len(cf.Metrics))
for name := range cf.Metrics {
metricNames = append(metricNames, name)
}
sort.Strings(metricNames)
for _, metricName := range metricNames {
cm := cf.Metrics[metricName]
ts := cm.Start
for _, v := range cm.Data {
if !v.IsNaN() {
w.batch = append(w.batch, ParquetMetricRow{
Cluster: cluster,
Hostname: hostname,
Metric: metricName,
Scope: scope,
ScopeID: scopeID,
Timestamp: ts,
Frequency: cm.Frequency,
Value: float32(v),
})
if len(w.batch) >= parquetBatchSize {
w.writer.Write(w.batch)
w.count += len(w.batch)
w.batch = w.batch[:0]
}
}
ts += cm.Frequency
}
}
// Sort child names for deterministic order
childNames := make([]string, 0, len(cf.Children))
for name := range cf.Children {
childNames = append(childNames, name)
}
sort.Strings(childNames)
for _, childName := range childNames {
childScope, childScopeID := parseScopeFromName(childName)
w.writeLevel(cf.Children[childName], cluster, hostname, childScope, childScopeID)
}
}
// Close finalises the Parquet file (footer, buffered I/O, file handle).
func (w *parquetArchiveWriter) Close() error {
if err := w.writer.Close(); err != nil {
@@ -159,16 +183,6 @@ func (w *parquetArchiveWriter) Close() error {
return w.f.Close()
}
// sortParquetRows sorts rows by (metric, timestamp) in-place.
func sortParquetRows(rows []ParquetMetricRow) {
sort.Slice(rows, func(i, j int) bool {
if rows[i].Metric != rows[j].Metric {
return rows[i].Metric < rows[j].Metric
}
return rows[i].Timestamp < rows[j].Timestamp
})
}
// loadCheckpointFileFromDisk reads a JSON or binary checkpoint file and returns
// a CheckpointFile. Used by the Parquet archiver to read checkpoint data
// before converting it to Parquet format.
@@ -218,22 +232,10 @@ func loadCheckpointFileFromDisk(filename string) (*CheckpointFile, error) {
}
}
// estimateRowCount estimates the number of Parquet rows a CheckpointFile will produce.
// Used for pre-allocating the rows slice to avoid repeated append doubling.
func estimateRowCount(cf *CheckpointFile) int {
n := 0
for _, cm := range cf.Metrics {
n += len(cm.Data)
}
for _, child := range cf.Children {
n += estimateRowCount(child)
}
return n
}
// archiveCheckpointsToParquet reads checkpoint files for a host directory,
// converts them to Parquet rows. Returns the rows and filenames that were processed.
func archiveCheckpointsToParquet(dir, cluster, host string, from int64) ([]ParquetMetricRow, []string, error) {
// loadCheckpointFiles reads checkpoint files for a host directory and returns
// the loaded CheckpointFiles and their filenames. Processes one file at a time
// to avoid holding all checkpoint data in memory simultaneously.
func loadCheckpointFiles(dir string, from int64) ([]*CheckpointFile, []string, error) {
entries, err := os.ReadDir(dir)
if err != nil {
return nil, nil, err
@@ -248,36 +250,18 @@ func archiveCheckpointsToParquet(dir, cluster, host string, from int64) ([]Parqu
return nil, nil, nil
}
// First pass: load checkpoints and estimate total rows for pre-allocation.
type loaded struct {
cf *CheckpointFile
filename string
}
var checkpoints []loaded
totalEstimate := 0
var checkpoints []*CheckpointFile
var processedFiles []string
for _, checkpoint := range files {
filename := filepath.Join(dir, checkpoint)
cf, err := loadCheckpointFileFromDisk(filename)
if err != nil {
cclog.Warnf("[METRICSTORE]> skipping unreadable checkpoint %s: %v", filename, err)
continue
}
totalEstimate += estimateRowCount(cf)
checkpoints = append(checkpoints, loaded{cf: cf, filename: checkpoint})
checkpoints = append(checkpoints, cf)
processedFiles = append(processedFiles, checkpoint)
}
if len(checkpoints) == 0 {
return nil, nil, nil
}
rows := make([]ParquetMetricRow, 0, totalEstimate)
processedFiles := make([]string, 0, len(checkpoints))
for _, cp := range checkpoints {
rows = flattenCheckpointFile(cp.cf, cluster, host, "node", "", rows)
processedFiles = append(processedFiles, cp.filename)
}
return rows, processedFiles, nil
return checkpoints, processedFiles, nil
}