docs/content/pypaimon/data-evolution.md

---
title: "Data Evolution"
weight: 5
type: docs
aliases:
  - /pypaimon/data-evolution.html
---

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# Data Evolution

PyPaimon for Data Evolution mode. See [Data Evolution]({{< ref "append-table/data-evolution" >}}).

## Prerequisites

To use partial updates / data evolution, enable both options when creating the table:

- **`row-tracking.enabled`**: `true`
- **`data-evolution.enabled`**: `true`

## Update Columns By Row ID

You can create `TableUpdate.update_by_arrow_with_row_id` to update columns to data evolution tables.

The input data should include the `_ROW_ID` column, update operation will automatically sort and match each `_ROW_ID` to
its corresponding `first_row_id`, then groups rows with the same `first_row_id` and writes them to a separate file.

**Requirements for `_ROW_ID` updates**

- **All rows required**: the input table must contain **exactly the full table row count** (one row per existing row).
- **Row id coverage**: after sorting by `_ROW_ID`, it must be **0..N-1** (no duplicates, no gaps).
- **Update columns only**: include `_ROW_ID` plus the columns you want to update (partial schema is OK).

```python
import pyarrow as pa
from pypaimon import CatalogFactory, Schema

catalog = CatalogFactory.create({'warehouse': '/tmp/warehouse'})
catalog.create_database('default', False)

simple_pa_schema = pa.schema([
  ('f0', pa.int8()),
  ('f1', pa.int16()),
])
schema = Schema.from_pyarrow_schema(simple_pa_schema,
                                    options={'row-tracking.enabled': 'true', 'data-evolution.enabled': 'true'})
catalog.create_table('default.test_row_tracking', schema, False)
table = catalog.get_table('default.test_row_tracking')

# write all columns
write_builder = table.new_batch_write_builder()
table_write = write_builder.new_write()
table_commit = write_builder.new_commit()
expect_data = pa.Table.from_pydict({
  'f0': [-1, 2],
  'f1': [-1001, 1002]
}, schema=simple_pa_schema)
table_write.write_arrow(expect_data)
table_commit.commit(table_write.prepare_commit())
table_write.close()
table_commit.close()

# update partial columns
write_builder = table.new_batch_write_builder()
table_update = write_builder.new_update().with_update_type(['f0'])
table_commit = write_builder.new_commit()
data2 = pa.Table.from_pydict({
  '_ROW_ID': [0, 1],
  'f0': [5, 6],
}, schema=pa.schema([
  ('_ROW_ID', pa.int64()),
  ('f0', pa.int8()),
]))
cmts = table_update.update_by_arrow_with_row_id(data2)
table_commit.commit(cmts)
table_commit.close()

# content should be:
#   'f0': [5, 6],
#   'f1': [-1001, 1002]
```

## Filter by _ROW_ID

Requires the same [Prerequisites](#prerequisites) (row-tracking and data-evolution enabled). On such tables you can filter by `_ROW_ID` to prune files at scan time. Supported: `equal('_ROW_ID', id)`, `is_in('_ROW_ID', [id1, ...])`, `between('_ROW_ID', low, high)`.

```python
pb = table.new_read_builder().new_predicate_builder()
rb = table.new_read_builder().with_filter(pb.equal('_ROW_ID', 0))
result = rb.new_read().to_arrow(rb.new_scan().plan().splits())
```

## Update Columns By Shards

If you want to **compute a derived column** (or **update an existing column based on other columns**) without providing
`_ROW_ID`, you can use the shard scan + rewrite workflow:

- Read only the columns you need (projection)
- Compute the new values in the same row order
- Write only the updated columns back
- Commit per shard

This is useful for backfilling a newly added column, or recomputing a column from other columns.

**Example: compute `d = c + b - a`**

```python
import pyarrow as pa
from pypaimon import CatalogFactory, Schema

catalog = CatalogFactory.create({'warehouse': '/tmp/warehouse'})
catalog.create_database('default', False)

table_schema = pa.schema([
    ('a', pa.int32()),
    ('b', pa.int32()),
    ('c', pa.int32()),
    ('d', pa.int32()),
])

schema = Schema.from_pyarrow_schema(
    table_schema,
    options={'row-tracking.enabled': 'true', 'data-evolution.enabled': 'true'},
)
catalog.create_table('default.t', schema, False)
table = catalog.get_table('default.t')

# write initial data (a, b, c only)
write_builder = table.new_batch_write_builder()
write = write_builder.new_write().with_write_type(['a', 'b', 'c'])
commit = write_builder.new_commit()
write.write_arrow(pa.Table.from_pydict({'a': [1, 2], 'b': [10, 20], 'c': [100, 200]}))
commit.commit(write.prepare_commit())
write.close()
commit.close()

# shard update: read (a, b, c), write only (d)
update = write_builder.new_update()
update.with_read_projection(['a', 'b', 'c'])
update.with_update_type(['d'])

shard_idx = 0
num_shards = 1
upd = update.new_shard_updator(shard_idx, num_shards)
reader = upd.arrow_reader()

for batch in iter(reader.read_next_batch, None):
    a = batch.column('a').to_pylist()
    b = batch.column('b').to_pylist()
    c = batch.column('c').to_pylist()
    d = [ci + bi - ai for ai, bi, ci in zip(a, b, c)]

    upd.update_by_arrow_batch(
        pa.RecordBatch.from_pydict({'d': d}, schema=pa.schema([('d', pa.int32())]))
    )

commit_messages = upd.prepare_commit()
commit = write_builder.new_commit()
commit.commit(commit_messages)
commit.close()
```

**Example: update an existing column `c = b - a`**

```python
update = write_builder.new_update()
update.with_read_projection(['a', 'b'])
update.with_update_type(['c'])

upd = update.new_shard_updator(0, 1)
reader = upd.arrow_reader()
for batch in iter(reader.read_next_batch, None):
    a = batch.column('a').to_pylist()
    b = batch.column('b').to_pylist()
    c = [bi - ai for ai, bi in zip(a, b)]
    upd.update_by_arrow_batch(
        pa.RecordBatch.from_pydict({'c': c}, schema=pa.schema([('c', pa.int32())]))
    )

commit_messages = upd.prepare_commit()
commit = write_builder.new_commit()
commit.commit(commit_messages)
commit.close()
```

**Notes**

- **Row order matters**: the batches you write must have the **same number of rows** as the batches you read, in the
  same order for that shard.
- **Parallelism**: run multiple shards by calling `new_shard_updator(shard_idx, num_shards)` for each shard.