mirror of
https://github.com/ClusterCockpit/cc-backend
synced 2026-03-24 00:27:29 +01:00
Jan Eitzinger
688d41d11a
Entire-Session: 0943a044-b17e-4215-8591-c1a0c816ddf0 Entire-Strategy: manual-commit Entire-Agent: Claude Code Ephemeral-branch: entire/3314b8e-e3b0c4
105 lines
3.9 KiB
Plaintext
105 lines
3.9 KiB
Plaintext
Implement the following plan:
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# Fix: Memory Escalation in flattenCheckpointFile (68GB+)
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## Context
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Production gops shows `flattenCheckpointFile` allocating 68GB+ (74.89% of memory). The archiving pipeline accumulates ALL metric data from ALL hosts into a single `[]ParquetMetricRow` slice before writing to Parquet. For large HPC clusters this is catastrophic. Additionally, the `SortingWriterConfig` in the parquet writer buffers everything again internally.
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## Root Cause
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Two-layer unbounded accumulation:
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1. **`archive.go:239-242`**: `allRows = append(allRows, r.rows...)` merges every host's rows into one giant slice
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2. **`parquetArchive.go:108-116`**: `SortingWriterConfig` creates a sorting writer that buffers ALL rows until `Close()`
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3. **`parquetArchive.go:199`**: `var rows []ParquetMetricRow` starts at zero capacity, grows via append doubling
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Peak memory = (all hosts' rows) + (sorting writer copy) + (append overhead) = ~3x raw data size.
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## Fix: Stream per-host to parquet writer
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Instead of accumulating all rows, write each host's data as a separate row group.
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### Step 1: Add streaming parquet writer (`parquetArchive.go`)
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Replace `writeParquetArchive(filename, rows)` with a struct that supports incremental writes:
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```go
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type parquetArchiveWriter struct {
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writer *pq.GenericWriter[ParquetMetricRow]
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bw *bufio.Writer
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f *os.File
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count int
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}
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func newParquetArchiveWriter(filename string) (*parquetArchiveWriter, error)
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func (w *parquetArchiveWriter) WriteHostRows(rows []ParquetMetricRow) error // Write + Flush (creates row group)
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func (w *parquetArchiveWriter) Close() error
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```
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- **Remove `SortingWriterConfig`** - no global sort buffer
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- Sort each host's rows in-place with `sort.Slice` before writing (cheap: single host data)
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- Each `Flush()` creates a separate row group per host
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### Step 2: Add row count estimation (`parquetArchive.go`)
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```go
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func estimateRowCount(cf *CheckpointFile) int
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```
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Pre-allocate `rows` slice in `archiveCheckpointsToParquet` to avoid append doubling per host.
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### Step 3: Restructure `archiveCheckpoints` (`archive.go`)
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Change from:
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```
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workers → channel → accumulate allRows → writeParquetArchive(allRows)
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```
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To:
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```
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open writer → workers → channel → for each host: sort rows, writer.WriteHostRows(rows) → close writer
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```
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- Only one host's rows in memory at a time
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- Track `files`/`dir` for deletion separately (don't retain rows)
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- Check `writer.count > 0` instead of `len(allRows) == 0`
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### Step 4: Update test (`parquetArchive_test.go`)
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- `TestParquetArchiveRoundtrip`: use new streaming writer API
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- Keep `archiveCheckpointsToParquet` returning rows (it's per-host, manageable size)
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## Files to Modify
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- **`pkg/metricstore/parquetArchive.go`**: Add `parquetArchiveWriter`, `estimateRowCount`; remove `writeParquetArchive`; add `"sort"` import
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- **`pkg/metricstore/archive.go`**: Restructure `archiveCheckpoints` to stream
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- **`pkg/metricstore/parquetArchive_test.go`**: Update roundtrip test
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## Memory Impact
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- **Before**: All hosts in memory (~40GB for 256 nodes) + sorting buffer (~40GB) = 68GB+
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- **After**: One host at a time (~16MB) + parquet page buffer (~1MB) = ~17MB peak
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## Sorting Tradeoff
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The output changes from one globally-sorted row group to N row groups (one per host), each internally sorted by (metric, timestamp). This is actually better for ClusterCockpit's per-host query patterns (enables row group skipping).
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## Verification
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```bash
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go test -v ./pkg/metricstore/...
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```
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Also verify with `go vet ./pkg/metricstore/...` for correctness.
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If you need specific details from before exiting plan mode (like exact code snippets, error messages, or content you generated), read the full transcript at: /Users/jan/.claude/projects/-Users-jan-prg-CC-cc-backend/71340843-de3d-4e83-9dcb-2fc130c50e0d.jsonl
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---
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Are the any other cases with memory spikes using the Parquet Writer, e.g. in the nodestate retention?
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---
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[Request interrupted by user for tool use] |