apache / apache/iceberg-python

Allow user to define a subset of columns for update detection in UPSERT

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Python
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PR mergées (30 j)
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Description

### Feature Request / Improvement

Currently, when detecting which rows should be updated in the `upsert`, all non-primary key columns are iterated over, converted to a Python type, and compared. This can be time-consuming and memory-consuming (e.g., with complex columns containing JSON data in `struct`, `list`, ...).

If the user knows that a change has occurred to specific columns, it would be a huge performance improvement to just iterate over these columns. Or if the user has a column that implies that any change has occurred (e.g., a hash of the data)

For example:
Hash column: if the user has the possibility to create a column containing a hash for each row, then upsert has to look only at this column when detecting changes. This way, pyiceberg doesn't have to convert all columns to Python type and compare them.

Proposition:

Update the function `get_rows_to_update` to also accept an optional parameter `difference_cols`. Update the upsert methods with this parameter and pass it to the `get_rows_to_update`.

In case there is no intersection between non-primary key columns and `difference_cols`, `pyiceberg` can either raise and error or it can fall-back to the default behaviour (iterating over all non-PK columns).

Usage:

```python
from pyiceberg.schema import Schema
from pyiceberg.types import IntegerType, NestedField, StringType

import pyarrow as pa

schema = Schema(
NestedField(1, "city", StringType(), required=True),
NestedField(2, "inhabitants", IntegerType(), required=True),
# Mark City as the identifier field, also known as the primary-key
identifier_field_ids=[1]
)

tbl = catalog.create_table("default.cities", schema=schema)

arrow_schema = pa.schema(
[
pa.field("city", pa.string(), nullable=False),
pa.field("inhabitants", pa.int32(), nullable=False),
]
)

# Write some data
df = pa.Table.from_pylist(
[
{"city": "Amsterdam", "inhabitants": 921402},
{"city": "San Francisco", "inhabitants": 808988},
{"city": "Drachten", "inhabitants": 45019},
{"city": "Paris", "inhabitants": 2103000},
],
schema=arrow_schema
)
tbl.append(df)

df = pa.Table.from_pylist(
[
# Will be updated, the inhabitants has been updated
{"city": "Drachten", "inhabitants": 45505},

# New row, will be inserted
{"city": "Berlin", "inhabitants": 3432000},

# Ignored, already exists in the table
{"city": "Paris", "inhabitants": 2103000},
],
schema=arrow_schema
)
upd = tbl.upsert(df, difference_cols=["inhabitants"])
```

I have already prepared how it can look in my fork 59d18337a61b106566c2e6a432b7d4899ca7f334.
If the proposition is accepted, I can prepare the PR.

Guide de contribution

Aucun guide de contribution indexé pour ce dépôt

Piste de recherche

Commencez par examiner get_rows_to_update et les méthodes upsert, puis comparez le comportement proposé avec le commit 59d18337a61b106566c2e6a432b7d4899ca7f334. Ajoutez la gestion facultative de difference_cols afin que les colonnes sélectionnées qui ne sont pas des clés primaires déterminent la détection des mises à jour, et confirmez le comportement choisi lorsqu’aucune des colonnes demandées ne correspond aux colonnes disponibles.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

Évaluation

Stack technique
python
Domaine
data-engineering, databases
Type d'issue
Fonctionnalité
Difficulté
3/5
Temps estimé
1-2 jours
Activité
Calme
Clarté
Plutôt claire
Accessibilité débutants
55/100

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