---
phase: 25-lazy-evaluation-cache-efficiency
verified: 2026-03-27T22:15:00Z
status: passed
score: 2/2 must-haves verified
re_verification: false
human_verification: []
---

# Phase 25: Lazy Evaluation + Cache Efficiency Verification Report

**Phase Goal:** Replace eager full-file loads with lazy scans and eliminate unnecessary copy operations
**Verified:** 2026-03-27T22:15:00Z
**Status:** passed
**Re-verification:** No — initial verification

---

## Goal Achievement

### Observable Truths

| #   | Truth                                                                                           | Status   | Evidence                                                                                   |
| --- | ----------------------------------------------------------------------------------------------- | -------- | ------------------------------------------------------------------------------------------ |
| 1   | `write_ticks` dedup check reads only `agg_trade_id` column (not all 7) for anti-join comparison | VERIFIED | `pl.read_parquet(parquet_path, columns=["agg_trade_id"])` at line 284                      |
| 2   | Full file load is deferred — only happens when new rows exist after anti-join                   | VERIFIED | `if not write_new.is_empty(): existing_df = pl.read_parquet(parquet_path)` at line 291-293 |
| 3   | Stathera diagnostic in `_sync_flush_rest_bars` uses in-place sort instead of `sorted()` copy    | VERIFIED | `batch_bars.sort(key=lambda b: b.get("first_agg_trade_id", 0))` at line 618                |

**Score:** 3/3 observable truths verified (2/2 requirements satisfied)

---

### Required Artifacts

| Artifact                                      | Expected                                | Status   | Details                                                                         |
| --------------------------------------------- | --------------------------------------- | -------- | ------------------------------------------------------------------------------- |
| `python/opendeviationbar/storage/parquet.py`  | Column-projected dedup in `write_ticks` | VERIFIED | `read_parquet(columns=["agg_trade_id"])` at line 284; `del existing_ids` at 290 |
| `python/opendeviationbar/sidecar/midnight.py` | In-place sort in Stathera diagnostic    | VERIFIED | `batch_bars.sort(key=...)` at line 618                                          |

---

### Key Link Verification

| From                       | To                              | Via                              | Status | Details                                                           |
| -------------------------- | ------------------------------- | -------------------------------- | ------ | ----------------------------------------------------------------- |
| `write_ticks` dedup branch | column-projected `read_parquet` | `columns=["agg_trade_id"]` param | WIRED  | Line 284: reads 1/7 columns; anti-join on `agg_trade_id`          |
| dedup anti-join result     | conditional full-file load      | `if not write_new.is_empty()`    | WIRED  | Lines 291-293: full `read_parquet` only when merge needed         |
| Stathera diagnostic loop   | in-place `list.sort()`          | `batch_bars.sort(key=...)`       | WIRED  | Line 618: sorts the `batch_bars` list in-place, no copy allocated |

---

### Data-Flow Trace (Level 4)

Not applicable — both changes are optimizations to I/O and memory allocation patterns, not components that render or expose dynamic data. No data-flow hollow-prop risk.

---

### Behavioral Spot-Checks

| Behavior                                        | Command                                                                | Result                    | Status |
| ----------------------------------------------- | ---------------------------------------------------------------------- | ------------------------- | ------ |
| LAZY-01: `columns=` param present in parquet.py | `grep -n "columns=\[\"agg_trade_id\"\]" python/.../storage/parquet.py` | line 284 found            | PASS   |
| LAZY-01: full load gated on non-empty anti-join | `grep -n "write_new.is_empty" python/.../storage/parquet.py`           | line 291 found            | PASS   |
| LAZY-02: `list.sort()` present in midnight.py   | `grep -n "batch_bars.sort" python/.../sidecar/midnight.py`             | line 618 found            | PASS   |
| LAZY-02: no `sorted(batch_bars` remains         | `grep -n "sorted(batch_bars" python/.../sidecar/midnight.py`           | 0 matches                 | PASS   |
| Both commits verified in git                    | `git show --stat 79fa9c8 7740f06`                                      | both exist, correct files | PASS   |

---

### Requirements Coverage

| Requirement | Source Plan   | Description                                                                  | Status    | Evidence                                                                                           |
| ----------- | ------------- | ---------------------------------------------------------------------------- | --------- | -------------------------------------------------------------------------------------------------- |
| LAZY-01     | 25-01-PLAN.md | `write_ticks` dedup uses column projection for ID-only check (not full load) | SATISFIED | `pl.read_parquet(parquet_path, columns=["agg_trade_id"])` at parquet.py:284; commit 79fa9c8        |
| LAZY-02     | 25-01-PLAN.md | Stathera diagnostic sort uses in-place sort, avoids `sorted()` copy          | SATISFIED | `batch_bars.sort(key=lambda b: b.get("first_agg_trade_id", 0))` at midnight.py:618; commit 7740f06 |

**Note on REQUIREMENTS.md checkbox state:** Both LAZY-01 and LAZY-02 appear with unchecked `- [ ]` checkboxes and "Pending" status in `.planning/REQUIREMENTS.md`. This is a documentation artifact — the implementation is complete and verified in code. The REQUIREMENTS.md tracking table was not updated as part of this phase. Not a code gap, but the tracking file should be updated.

**Note on LAZY-01 implementation approach:** The PLAN specified `pl.scan_parquet(parquet_path).select("agg_trade_id").collect()`. The implementation used `pl.read_parquet(parquet_path, columns=["agg_trade_id"])` instead. The SUMMARY documents this as a deliberate deviation: Polars type stubs return `InProcessQuery | DataFrame` from `.collect()`, causing type-checker errors. The `columns=` parameter achieves identical column projection (reads only 1/7 columns) with clean types. The goal of the requirement is fully satisfied — ID-only reads for dedup anti-join.

---

### Anti-Patterns Found

| File | Line | Pattern    | Severity | Impact |
| ---- | ---- | ---------- | -------- | ------ |
| —    | —    | None found | —        | —      |

No TODOs, FIXMEs, placeholders, empty return stubs, or hardcoded-empty data found in either modified file.

---

### Human Verification Required

None. Both changes are structural code optimizations verifiable entirely through static analysis.

---

### Gaps Summary

No gaps. Both requirements are implemented correctly and verified in code:

- **LAZY-01** (parquet.py:284): `write_ticks` dedup path reads only the `agg_trade_id` column using `read_parquet(columns=["agg_trade_id"])`. Full file load at line 293 is correctly gated behind `if not write_new.is_empty()`. The `del existing_ids` at line 290 additionally releases the projected frame as soon as the anti-join completes.

- **LAZY-02** (midnight.py:618): The Stathera diagnostic loop calls `batch_bars.sort(key=lambda b: b.get("first_agg_trade_id", 0))` — an in-place sort that mutates the existing list rather than allocating a copy. No `sorted(batch_bars, ...)` pattern remains anywhere in the file.

The only administrative item is that `.planning/REQUIREMENTS.md` still shows both IDs as "Pending" — the code is done but the tracking file was not updated.

---

_Verified: 2026-03-27T22:15:00Z_
_Verifier: Claude (gsd-verifier)_
