pyhoglake

Python client for hoglake, the Postgres-native lakehouse-catalog control plane. A thin API wrapper: no embedded engine, no SQL, no direct catalog-database access — ever. The client writes parquet to object storage itself and registers it with the control plane via footer-shipping commits.

Install

pip install pyhoglake                  # or: uv add pyhoglake
pip install 'pyhoglake[fast-upload]'   # + boto3, for single-request uploads

Dependencies: httpx, pyarrow, thrift. The fast-upload extra adds boto3, which the writer path uses to put a small parquet object in ONE request (see Prepared appends); without it every object takes pyarrow's three-request multipart write, and pyhoglake logs one warning saying so. Development uses the flox env in this directory:

flox activate -- uv sync
flox activate -- uv run pytest                      # unit + integration
flox activate -- uv run pytest -m "not integration" # unit only

Integration tests need a live server (HOGLAKE_URL, default http://localhost:8080) and S3 credentials (HOGLAKE_S3_ENDPOINT, HOGLAKE_S3_ACCESS_KEY, HOGLAKE_S3_SECRET_KEY); they skip cleanly when the server is unreachable.

Quickstart — the append path end to end

import pyarrow as pa
from pyhoglake import HoglakeClient, S3Config

client = HoglakeClient(
    "http://localhost:8080",
    s3=S3Config(
        access_key="hoglake",
        secret_key="hoglake123",
        endpoint_override="http://localhost:9000",  # MinIO; omit for AWS
        region="us-east-1",
    ),
)

catalog = client.create_catalog("demo", "s3://my-bucket/demo/")
ns = catalog.create_namespace("analytics")

table = ns.create_table(
    "events",
    pa.schema(
        [
            pa.field("id", pa.int64(), nullable=False),
            pa.field("name", pa.string()),
            pa.field("amount", pa.decimal128(10, 2)),
        ]
    ),
)

# THE writer path: writes one parquet file (with catalog field ids
# embedded in the parquet schema) to
#   s3://my-bucket/demo/data/analytics/events/<uuid>.parquet
# extracts per-column footer stats (value/null counts, Iceberg
# single-value binary min/max bounds), and registers the file in one
# commit. The server never opens the file.
result = table.append(
    pa.table({"id": [1, 2], "name": ["a", None], "amount": [None, None]}),
    author="me",
    message="first batch",
)
print(result.snapshot_id)

# reads are metadata-only planning; you fetch the parquet yourself
for f in table.files():
    print(f.path, f.record_count, f.stats_state, f.row_id_start)

# changefeed + consumer offsets
plan = table.changes(from_snapshot=0)
catalog.commit_offset("my-consumer", table.table_uuid, plan.to_snapshot)
catalog.offset("my-consumer", table.table_uuid)  # one offset; None if unset

More surface:

from pyhoglake import ops

table.alter([ops.add_column("score", pa.float64())])  # schema evolution
table.info(snapshot=5)  # time travel
table.files(at_timestamp=some_datetime)  # by timestamp
table.append(big_table, deferred_stats=True)  # register as pending
catalog.set_retention(7 * 86400, consumer_floor=True)  # retention policy
catalog.expire()
catalog.cleanup()  # maintenance sweeps
report = catalog.verify()  # metadata-only invariant scan (read-only)
for c in report.failures:  # () when report.passed
    print(c.check, c.violations, c.description, c.samples)
ns.create_view("v", "SELECT 1", dialect="trino")
for s in catalog.snapshots(limit=1000):
    ...  # auto-paginated
for s in catalog.snapshots(before=head + 1):
    ...  # descending walk
    # (mutually exclusive
    # with non-zero after)

Configuration

Type mapping

The Arrow writer path maps 26 of the catalog's 27 wire names, both directions. variant is the exception: Arrow cannot construct it, so a variant column arrives only through Table.prepare_append_files (see "Native VARIANT files" below). An Arrow type outside the table is rejected with an error listing the supported set.

uuid columns: the wire form, and the two spellings

A hoglake uuid column is parquet FIXED_LEN_BYTE_ARRAY(16) carrying the UUID logical annotation (docs/iceberg-federation.md) — what server-side compaction writes on every file it rewrites, and the form an Iceberg-conformant reader needs to see a UUID rather than opaque bytes. pyarrow stamps that annotation only for its canonical uuid extension type, so coltype_to_arrow("uuid") returns pa.uuid() and every file this client writes is annotated. It needs pyarrow >= 21 (the package floor): pa.uuid() exists from 18, but 18 through 20 write the bytes with no annotation.

Both spellings are accepted everywhere on the way in:

• Table.append takes pa.uuid() or plain pa.binary(16) — the batch is cast to the catalog's schema, and the 16 bytes are the same either way.
• Table.prepare_append_files accepts a file whose uuid column is annotated or bare. A hoglake table holds both: compaction outputs have always been annotated, while files this client registered before the contract — and any writer below the pyarrow floor, or one that simply does not annotate — carry the bare form. Nothing else about the schema check is loosened, so a file with the right type and the wrong PARQUET:field_id is refused exactly as before.
• Reading, arrow_type_to_coltype maps both to uuid, and footer bounds are read from either (the bytes are unsigned-lexicographic in both).

Identifiers (namespace/table/view/column names) must match ^[A-Za-z_][A-Za-z0-9_-]{0,127}$ — the server 422s anything else, and the constraint is also a CHECK in its schema; catalog names are stricter (lower-case start, max 63).

Column names starting with _hog are additionally reserved for hoglake internals (_hog_row_id is compaction's row-id carrier) — the server 422s them at create/add/rename, and the client fast-fails them at table-create and append time before any request or upload; namespace/table/view names are not affected. Deletion-vector positions are per-file physical row ordinals (0-based position within that parquet file), not row ids.

Partitioned writes — client-side transforms, fanout appends

When a table has a live partition spec, Table.append computes each row's partition tuple client-side (the server never opens data files), splits the batch by tuple, writes one parquet file per partition, and registers them all in one atomic commit — each file carrying its partition_values (transformed values as strings, by key_index). The coarse-grained layout the near-term consumers use is months per team:

from pyhoglake import ops

table = ns.create_table(
    "events",
    pa.schema(
        [
            pa.field("team_id", pa.int64(), nullable=False),
            pa.field("ts", pa.timestamp("us")),
            pa.field("payload", pa.string()),
        ]
    ),
)
fid = {c.name: c.field_id for c in table.columns}
table.alter(
    [
        ops.set_partition_spec(
            [
                ops.partition_field(fid["team_id"], "identity"),
                ops.partition_field(fid["ts"], "month"),
            ]
        )
    ]
)

# a batch spanning 3 months x 2 teams -> 6 files, ONE commit
res = table.append(batch)
for f in res.files:  # AppendResult exposes the computed tuples
    print(f.path, f.record_count, f.partition_values)
    # ('101', '672') = identity(team_id)=101, month(ts)=2026-01
    # (months are epoch-relative ints per Iceberg: 672 = (2026-1970)*12)

Transforms (pyhoglake.transforms) follow the Iceberg spec exactly and are pinned against its published test vectors:

A null source value yields a null partition value forming its own partition group (Iceberg semantics). The tuple is computed under the spec the client resolved (Table.append re-resolves pre-flight; prepare_append_files uses its cached read). If the spec changes before the commit lands, the server refuses the commit — 409 ddl_since_read_snapshot, atomically and with zero writes — and the client never silently recomputes under a different spec. That refusal is also why an append whose files carry partition_values must send a read_snapshot: without one the commit has no conflict window, so the spec change could not be detected at all. The server will answer 422 once HOGLAKE_REFUSE_BLIND_PARTITIONED_APPENDS is flipped; today it accepts the shape, WARNs once per resolved table and counts hoglake_blind_partitioned_appends_total. pyhoglake supplies the basis itself, so a caller never has to. Grouping runs arrow-native where possible and per unique value (never per row) otherwise. Compaction groups only within (spec_id, partition_values) server-side, so partition-local file layout is preserved end to end.

Prepared appends — buffered encode, one-request uploads, one commit

A writer that owns its own partitioning and sort order (the events writer flushes ~105K rows fanned out over ~271 partition tuples) prepares its files itself and publishes them in a separate, idempotent step:

key = str(uuid.uuid4())  # this prepare's idempotency key
# ... or prepare_append_files([(path, partition_tuple), ...])
request = table.prepare_append_tables(
    [(arrow_table, partition_tuple), ...],
    idempotency_key=key,
    expected_table_uuid=table.table_uuid,
)
persist(request)  # durably, BEFORE publishing
catalog.commit_prepared(request)  # idempotent: safe to retry

prepare_append_tables encodes each group to a parquet buffer in memory — nothing to write, fsync, re-read for the footer and unlink — and produces the same registrations prepare_append_files produces for the same rows. Use prepare_append_files for files another writer produced (native VARIANT, allow_optional_fields); Arrow tables are refused for a VARIANT destination, because an Arrow rewrite loses the annotation.

Deploy prerequisite. The single-request path is only active if boto3 is importable, so a writer that wants it must install pyhoglake[fast-upload] — a plain pyhoglake install keeps the three-request streaming path and pays ~3x the S3 requests per flush. When the extra is missing, or when botocore refuses the ambient AWS configuration, pyhoglake logs one warning per client on the pyhoglake logger naming the condition — so a process that configures logging hears about it, while the library itself only attaches a NullHandler and never writes to stderr uninvited. single_request_uploads=False is how to choose the streaming path deliberately, and it logs nothing.

The append incarnation guard — atomic at commit

Commit payloads are addressed by (namespace, table) name, so an append lands on whatever table currently holds that name. If the table is dropped and recreated (a new table_uuid) between your resolve and your append, a naive client would write into the new incarnation's history without noticing.

Table.append(..., expected_table_uuid=...) guards against this atomically, at commit time. Every commit carries an expected_table_uuid field (default: the table_uuid the Table object was resolved as; pass one explicitly to pin a specific incarnation), and the server rejects the whole commit with 409 table_recreated — zero writes — when the live table's uuid differs. The client maps that CODE to IncarnationChangedError (re_prepare=True); ordinary commit conflicts remain CommitConflictError (retryable). There is no window in which a recreated table can accept rows from a guarded append.

Table.append also keeps one cheap pre-flight re-resolve before the parquet upload. That is purely an optimization — it fast-fails an already-dead incarnation before paying for the S3 write — not the safety mechanism. prepare_append_files makes no such read when its cache is warm (see "The writer path's reads" below); the server-side guard is the same either way. A commit-time refusal orphans the uploaded parquet (cleanup's problem, never the catalog's). A refused append never rebases the Table object's pinned identity, so a blind retry trips the guard again rather than silently adopting the new incarnation.

To opt out entirely (name-only resolution), pass expected_table_uuid=pyhoglake.UNGUARDED; the commit then carries no expected_table_uuid field and no pre-flight check runs.

The writer path's reads

A flush used to cost two GETs before its commit: one on the catalog for a read_snapshot, and one on the table for its uuid, columns and spec. The second is the expensive one — the server's table response computes the table's live totals, a count(*) and two sums over every live file row of the table (hoglake#232) — and the writer never reads a total.

Both are gone from the steady state, and no new wire field was needed for it. Table caches the last TableInfo it read together with the snapshot that read resolved at (TableInfo.read_snapshot_id), and prepare_append_files prepares against the cache and sends that same snapshot as read_snapshot. The server's existing OCC then does exactly the validation the re-read was for: the commit is accepted iff nothing has altered, dropped or recreated the table since. Anything that has is one of the three re_prepare=True refusals, which drops the cache so the next prepare_* re-reads once.

The zero-GET steady state needs a server that returns TableInfo.read_snapshot_id, and a current server always does — it is required and non-null in the spec. An OLDER one sends nothing to use as a read_snapshot, so the cache is never used and the writer path makes the same two reads it always did (one of them cheaper, since it asks for identity only). Every row below is measured in tests on both sides of that, and test_metadata_parity.py pins the three cross-tree facts the fast path rests on: the server declares the field, declares it required, and documents the totals parameter.

The age refresh is the one thing the cache needs beyond invalidation: a read_snapshot older than the catalog's retention is below the expiry floor, and the resulting 410 arrives after the flush's parquet is uploaded — a re-encode and a set of orphaned objects each time. The cache therefore refreshes at half the retention (read once per Catalog from snapshot_retention_seconds; 30 minutes assumed when the catalog will not say, and never when retention is disabled). An old read_snapshot costs the server nothing otherwise: the conflict scan is an index range over one table's change rows.

Catalog.commit_prepared(payload, table=...) is what drops the cache on a re_prepare refusal, and Table.commit_prepared(payload) is the form to prefer — it passes the Table for you, so the invalidation cannot be forgotten. The Catalog form stays for the cross-process case the contract is built around (persist the payload, publish from anywhere, possibly after a restart); a caller on that form without table= owns invalidation itself, via Table.invalidate() or by dropping the Table. Not doing so turns a one-flush refusal into a loop until the cache ages out.

Reads a caller makes are untouched — table.info() still returns the totals. Only the writer path asks for identity alone, and expected_table_info= opts out of the cache entirely, because its contract is to compare the caller's layout against a fresh server read.

Not in 0.1

Deletion-vector writes and Iceberg-facade reads.

Comparison with pyiceberg

pyhoglake follows pyiceberg's ergonomics where they fit, but the architecture differs on purpose: the catalog is a service — pyhoglake is a thin REST client that owns only the writer path (parquet + footer stats), and everything transactional happens server-side.

Native VARIANT files

Catalog columns may use variant (Iceberg v3). Publish native Parquet VARIANT(1) files with Table.prepare_append_files and the existing prepared-commit API. The client validates top-level field IDs, native annotations, scalar types and required-column null counts, then uploads the original bytes. Arrow Table.append does not construct VARIANT; an Arrow rewrite loses the annotation.

VARIANT columns cannot be partition or sort keys, and have no whole-column statistics. Shredded child statistics are not published as catalog bounds. The server skips VARIANT tables during scalar compaction. Reader interoperability and the buffered-ingestion coordinator are separate work.