feat: add ParquetValidate mage target and ClickHouse querying docs

Adds a `mage parquetValidate` target that validates a Parquet recording
via clickhouse-local in Docker (schema presence, row count, seq/time_ns
sanity). Adds docs/parquet-querying.md with schema reference, invocation
pattern, and seven example queries with representative outputs.

Co-Authored-By: Claude Sonnet 4.6 (1M context) <noreply@anthropic.com>

1 files changed, 223 insertions, 0 deletions

diff --git a/docs/parquet-querying.md b/docs/parquet-querying.md
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+# Querying ior Parquet recordings with ClickHouse
+
+ior can record I/O events to a Parquet file (see `--record` flag). This document explains
+how to explore those recordings interactively using `clickhouse local`, which is bundled
+inside the standard `clickhouse/clickhouse-server` Docker image — no server, no persistent
+state, no installation needed beyond Docker.
+
+---
+
+## Prerequisites
+
+- Docker running locally (`docker info` must succeed)
+- A recording file, e.g. `ior-recording-20260313-170234.parquet`
+
+---
+
+## Schema
+
+| Column | Type | Description |
+|---|---|---|
+| `seq` | UInt64 | Monotonically increasing event sequence number |
+| `time_ns` | UInt64 | Absolute timestamp (nanoseconds since boot) |
+| `gap_ns` | UInt64 | Time since previous event (ns) |
+| `latency_ns` | UInt64 | Syscall duration (ns) |
+| `comm` | String | Process name |
+| `pid` | UInt32 | Process ID |
+| `tid` | UInt32 | Thread ID |
+| `syscall` | String | Syscall name (e.g. `read`, `openat`) |
+| `fd` | Int32 | File descriptor |
+| `ret` | Int64 | Return value (negative = errno) |
+| `bytes` | UInt64 | Bytes transferred (0 if not applicable) |
+| `file` | String | File path (empty if not resolved) |
+| `is_error` | Bool | True when `ret` is a negative errno |
+| `filter_epoch` | UInt64 | Filter generation at capture time |
+
+---
+
+## Running a query
+
+The general pattern mounts the directory containing the file as `/data` inside the container:
+
+```sh
+docker run --rm \
+  -v /path/to/recording/dir:/data:ro \
+  clickhouse/clickhouse-server:latest \
+  clickhouse local -q "SELECT ... FROM file('/data/recording.parquet', Parquet)"
+```
+
+For convenience, set shell variables:
+
+```sh
+FILE="ior-recording-20260313-170234.parquet"
+DIR="$(pwd)"   # or the absolute directory containing the file
+IMG="clickhouse/clickhouse-server:latest"
+
+docker run --rm -v "$DIR:/data:ro" "$IMG" clickhouse local -q \
+  "SELECT ... FROM file('/data/$FILE', Parquet)"
+```
+
+---
+
+## Example queries
+
+### Inspect the schema
+
+```sql
+DESCRIBE TABLE file('/data/recording.parquet', Parquet)
+```
+
+```
+seq           UInt64
+time_ns       UInt64
+gap_ns        UInt64
+latency_ns    UInt64
+comm          String
+pid           UInt32
+tid           UInt32
+syscall       String
+fd            Int32
+ret           Int64
+bytes         UInt64
+file          String
+is_error      Bool
+filter_epoch  UInt64
+```
+
+### Row count
+
+```sql
+SELECT count(*) FROM file('/data/recording.parquet', Parquet)
+```
+
+### Top syscalls by call count
+
+```sql
+SELECT syscall, count(*) AS n
+FROM file('/data/recording.parquet', Parquet)
+GROUP BY syscall
+ORDER BY n DESC
+LIMIT 15
+```
+
+```
+read        61800
+ioctl       14642
+statx       10916
+close        8660
+openat       6310
+write        6053
+...
+```
+
+### Error breakdown
+
+```sql
+SELECT syscall, ret, count(*) AS n
+FROM file('/data/recording.parquet', Parquet)
+WHERE is_error
+GROUP BY syscall, ret
+ORDER BY n DESC
+LIMIT 15
+```
+
+```
+read     -11   23597   -- EAGAIN (non-blocking, normal)
+statx     -2    1216   -- ENOENT
+ioctl    -25     540   -- ENOTTY
+openat    -2     376   -- ENOENT
+...
+```
+
+### Latency percentiles per syscall
+
+```sql
+SELECT
+    syscall,
+    count(*) AS n,
+    quantile(0.50)(latency_ns) AS p50_ns,
+    quantile(0.90)(latency_ns) AS p90_ns,
+    quantile(0.99)(latency_ns) AS p99_ns
+FROM file('/data/recording.parquet', Parquet)
+GROUP BY syscall
+ORDER BY p99_ns DESC
+LIMIT 15
+```
+
+```
+fdatasync    11   1745501   9444892   9994682   -- ~10ms p99, flushes to disk
+fallocate    31     35062    487162    589146
+rename        3    126619    170921    180889
+ftruncate    59      5449     35776    100399
+ioctl     14642      1155      8845     63626
+...
+```
+
+### Top files by I/O bytes
+
+```sql
+SELECT file, sum(bytes) AS total_bytes, count(*) AS ops
+FROM file('/data/recording.parquet', Parquet)
+WHERE file != ''
+GROUP BY file
+ORDER BY total_bytes DESC
+LIMIT 15
+```
+
+```
+/home/paul/.mozilla/firefox/.../cookies.sqlite-wal   7082880   432
+/dev/ptmx                                            1590757  1472
+/proc/3680458/smaps                                  1555387   419
+...
+```
+
+### Activity by process
+
+```sql
+SELECT comm, pid, count(*) AS n, sum(bytes) AS total_bytes
+FROM file('/data/recording.parquet', Parquet)
+GROUP BY comm, pid
+ORDER BY n DESC
+LIMIT 15
+```
+
+### Slow syscalls (above threshold)
+
+```sql
+SELECT time_ns, comm, pid, syscall, file, latency_ns
+FROM file('/data/recording.parquet', Parquet)
+WHERE latency_ns > 1000000   -- 1ms
+ORDER BY latency_ns DESC
+LIMIT 20
+```
+
+### Event timeline (10ms buckets)
+
+```sql
+SELECT
+    intDiv(time_ns, 10000000) AS bucket_10ms,
+    count(*) AS events,
+    sum(bytes) AS bytes
+FROM file('/data/recording.parquet', Parquet)
+GROUP BY bucket_10ms
+ORDER BY bucket_10ms
+```
+
+---
+
+## Automated validation
+
+The `mage parquetValidate` target runs schema, row-count, and sanity checks
+against the latest `*.parquet` in the repo root:
+
+```sh
+env GOTOOLCHAIN=auto mage parquetValidate
+
+# Or against a specific file:
+PARQUET_FILE=ior-recording-20260313-170234.parquet env GOTOOLCHAIN=auto mage parquetValidate
+```
+
+It checks:
+1. All 14 expected columns are present
+2. Row count > 0
+3. `seq` is monotonically ordered and `time_ns` is non-zero