amogh-jahagirdar commented on code in PR #16025:
URL: https://github.com/apache/iceberg/pull/16025#discussion_r3737189629
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format/spec.md:
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@@ -691,21 +707,118 @@ The `manifest_entry` struct consists of the following
fields:
| | _optional_ | **`4 file_sequence_number`** | `long`
| File sequence number indicating
when the file was added. Inherited when null and status is 1 (added). |
| _required_ | _required_ | **`2 data_file`** | `data_file`
`struct` (see below) | File path, partition tuple,
metrics, ... |
-The manifest entry fields are used to keep track of the snapshot in which
files were added or logically deleted. The `data_file` struct, defined below,
is nested inside the manifest entry so that it can be easily passed to job
planning without the manifest entry fields.
+ The manifest entry fields are used to keep track of the snapshot in which
files were added or logically deleted. The `data_file` struct, defined below,
is nested inside the manifest entry so that it can be easily passed to job
planning without the manifest entry fields.
-When a file is added to the dataset, its manifest entry should store the
snapshot ID in which the file was added and set status to 1 (added).
+ When a file is added to the dataset, its manifest entry should store the
snapshot ID in which the file was added and set status to 1 (added).
-When a file is replaced or deleted from the dataset, its manifest entry fields
store the snapshot ID in which the file was deleted and status 2 (deleted). The
file may be deleted from the file system when the snapshot in which it was
deleted is garbage collected, assuming that older snapshots have also been
garbage collected [1].
+ When a file is replaced or deleted from the dataset, its manifest entry
fields store the snapshot ID in which the file was deleted and status 2
(deleted). The file may be deleted from the file system when the snapshot in
which it was deleted is garbage collected, assuming that older snapshots have
also been garbage collected [1].
-Iceberg v2 adds data and file sequence numbers to the entry and makes the
snapshot ID optional. Values for these fields are inherited from manifest
metadata when `null`. That is, if the field is `null` for an entry, then the
entry must inherit its value from the manifest file's metadata, stored in the
manifest list.
-The `sequence_number` field represents the data sequence number and must never
change after a file is added to the dataset. The data sequence number
represents a relative age of the file content and should be used for planning
which delete files apply to a data file.
-The `file_sequence_number` field represents the sequence number of the
snapshot that added the file and must also remain unchanged upon assigning at
commit. The file sequence number can't be used for pruning delete files as the
data within the file may have an older data sequence number.
-The data and file sequence numbers are inherited only if the entry status is 1
(added). If the entry status is 0 (existing) or 2 (deleted), the entry must
include both sequence numbers explicitly.
+ Iceberg v2 adds data and file sequence numbers to the entry and makes the
snapshot ID optional. Values for these fields are inherited from manifest
metadata when `null`. That is, if the field is `null` for an entry, then the
entry must inherit its value from the manifest file's metadata, stored in the
manifest list.
+ The `sequence_number` field represents the data sequence number and must
never change after a file is added to the dataset. The data sequence number
represents a relative age of the file content and should be used for planning
which delete files apply to a data file.
+ The `file_sequence_number` field represents the sequence number of the
snapshot that added the file and must also remain unchanged upon assigning at
commit. The file sequence number can't be used for pruning delete files as the
data within the file may have an older data sequence number.
+ The data and file sequence numbers are inherited only if the entry status
is 1 (added). If the entry status is 0 (existing) or 2 (deleted), the entry
must include both sequence numbers explicitly.
-Notes:
+ Notes:
-1. Technically, data files can be deleted when the last snapshot that contains
the file as “live” data is garbage collected. But this is harder to detect and
requires finding the diff of multiple snapshots. It is easier to track what
files are deleted in a snapshot and delete them when that snapshot expires. It
is not recommended to add a deleted file back to a table. Adding a deleted file
can lead to edge cases where incremental deletes can break table snapshots.
-2. Manifest list files are required in v2, so that the `sequence_number` and
`snapshot_id` to inherit are always available.
+ 1. Technically, data files can be deleted when the last snapshot that
contains the file as "live" data is garbage collected. But this is harder to
detect and requires finding the diff of multiple snapshots. It is easier to
track what files are deleted in a snapshot and delete them when that snapshot
expires. It is not recommended to add a deleted file back to a table. Adding a
deleted file can lead to edge cases where incremental deletes can break table
snapshots.
+ 2. Manifest list files are required in v2, so that the `sequence_number`
and `snapshot_id` to inherit are always available.
+
+=== "v4"
+ **Content Entries**
+
+ | Field id | Name | Type | Write | Read | Description |
+ |----------|------|------|-------|------|-------------|
+ | 134 | **`content_type`** | `int` (0: DATA, 2: EQUALITY DELETES, 3:
DATA_MANIFEST, 4: DELETE_MANIFEST) | *required* | *required* | Type of content
stored in the entry. Content types 3 and 4 are only valid in root manifests. |
+ | 157 | **`format_version`** | `int` (0: PRE-V4, 4: V4) | *required* |
*required* | Writer format version. V4 writers must produce `format_version` 4.
|
+ | 100 | **`location`** | `string` | *required* | *required* | Location of
the file or manifest. |
+ | 101 | **`file_format`** | `string` | *required* | *required* | String
file format name: `avro`, `orc`, `parquet`, or `puffin` |
+ | 147 | **`tracking`** | `tracking` struct | *required* | *required* |
Groups status, snapshot, and sequence number. See tracking struct below. |
+ | 141 | **`spec_id`** | `int` | *optional* | *optional* | ID of the
partition spec used to write this manifest or data file. |
+ | 140 | **`sort_order_id`** | `int` | *optional* | *optional* | ID
representing sort order for this file. |
+ | 103 | **`record_count`** | `long` | *required* | *required* | Number of
records in this file. |
+ | 104 | **`file_size_in_bytes`** | `long` | *required* | *required* |
Total file size in bytes. |
+ | 146 | **`content_stats`** | `content_stats` struct | *optional* |
*optional* | Column stats. See [Column Stats
Improvements](#column-stats-improvements). |
+ | 150 | **`manifest_info`** | `manifest_info` struct | *optional* |
*optional* | See manifest_info struct below. |
+ | 131 | **`key_metadata`** | `binary` | *optional* | *optional* |
Implementation-specific key metadata for encryption. |
+ | 132 | **`split_offsets`** | `list<133: long>` | *optional* | *optional*
| Split offsets for the data or equality delete file. Must be sorted ascending.
|
+ | 135 | **`equality_ids`** | `list<136: int>` | *optional* | *optional* |
Field ids for row equality in equality delete files. |
+ | 148 | **`deletion_vector`** | `deletion_vector` struct | *optional* |
*optional* | Row-level deletion vector for a data file. |
+ | 158 | **`column_files`** | `list<159: column_file>` | *optional* |
*optional* | Column update files associated with this entry. |
+
+ Value 1 (POSITION_DELETES) is not used in v4. Writers must not produce
`content_type` 1.
+
+ V4 leaf data manifests must only contain entries with `content_type` 0
(DATA); V4 leaf delete manifests must only contain entries with `content_type`
2 (EQUALITY DELETES). A root manifest may reference V1-V3 manifests; V1-V3 leaf
manifest references must have `format_version` set to 0.
+
+ The following constraints apply based on `content_type`:
+
+ - `manifest_info` must be set when `content_type` is 3 or 4; must be null
otherwise.
+ - `deletion_vector` may only be set when `content_type` is 0; must be null
otherwise.
+ - `equality_ids` must be set when `content_type` is 2; must be null
otherwise.
+ - `column_files` must be null when `content_type` is not 0 or 3.
+ - `sort_order_id` must be null when `content_type` is 3 or 4 (manifests).
+ - `split_offsets` must be null when `content_type` is 3 or 4 (manifests).
+ - `tracking.deleted_positions` and `tracking.replaced_positions` must be
null when `content_type` is not 3 or 4.
+
+ **`tracking` struct (field 147)**
+
+ | Field id | Name | Type | Write | Read | Description |
+ |----------|------|------|-------|------|-------------|
+ | 0 | **`status`** | `int` (0: EXISTING, 1: ADDED, 2: DELETED, 3:
REPLACED, 4: MODIFIED) | *required* | *required* | Used to track additions,
deletions, replacements, and modifications. When a data file's
`deletion_vector` or `column_files` change, REPLACED marks the prior version of
the entry and MODIFIED marks the new, live version. For leaf manifest entries,
MODIFIED marks a live manifest whose `dv` changed. Deletes are not used in
scans. |
+ | 1 | **`snapshot_id`** | `long` | *optional* | *optional* | Snapshot ID
where the file was added or deleted. Inherited when null. Optional for leaf
manifests, required for root. |
+ | 5 | **`dv_snapshot_id`** | `long` | *optional* | *optional* | Snapshot
ID where the deletion vector was added. Inherited when null. Must be null when
`deletion_vector` is null. |
+ | 3 | **`sequence_number`** | `long` | *optional* | *optional* | Data
sequence number of the file. Inherited when null and status is 1 (ADDED). Must
equal `file_sequence_number` if `content_type` is 3 or 4. Optional for leaf
manifests, required for root. |
+ | 4 | **`file_sequence_number`** | `long` | *optional* | *optional* | File
sequence number indicating when the file was added. Inherited when null and
status is ADDED. Must equal `sequence_number` if `content_type` is 3 or 4. |
+ | 142 | **`first_row_id`** | `long` | *optional* | *optional* | The
`_row_id` for the first row in the data file if `content_type` is 0. If
`content_type` is 3, this is the starting `_row_id` to assign to rows added by
ADDED data files. See [First Row ID Inheritance](#first-row-id-inheritance). |
+ | 6 | **`deleted_positions`** | `binary` | *optional* | *optional* |
[TODO: link to roaring bitmap spec] Roaring bitmap of positions in the
referenced leaf manifest that were deleted in this snapshot. |
+ | 7 | **`replaced_positions`** | `binary` | *optional* | *optional* |
[TODO: link to roaring bitmap spec] Roaring bitmap of positions in the
referenced leaf manifest that were replaced in this snapshot. |
+
+ **`deletion_vector` struct (field 148)**
+
+ | Field id | Name | Type | Write | Read | Description |
+ |----------|------|------|-------|------|-------------|
+ | 155 | **`location`** | `string` | *required* | *required* | Location of
the Puffin file. |
+ | 144 | **`offset`** | `long` | *required* | *required* | Offset in the
file where the content starts. |
+ | 145 | **`size_in_bytes`** | `long` | *required* | *required* | Length of
the referenced content stored in the file. |
+ | 156 | **`cardinality`** | `long` | *required* | *required* | Cardinality
of the deletion vector. |
+ | 149 | **`key_metadata`** | `binary` | *optional* | *optional* |
Implementation-specific key metadata for encryption. |
+
+ **`manifest_info` struct (field 150)**
+
+ | Field id | Name | Type | Write | Read | Description |
+ |----------|------|------|-------|------|-------------|
+ | 504 | **`added_files_count`** | `long` | *required* | *required* | Count
of entries with status ADDED in the manifest. |
+ | 505 | **`existing_files_count`** | `long` | *required* | *required* |
Count of entries with status EXISTING in the manifest. |
+ | 506 | **`deleted_files_count`** | `long` | *required* | *required* |
Count of entries with status DELETED in the manifest. |
+ | 520 | **`replaced_files_count`** | `long` | *required* | *required* |
Count of entries with status REPLACED in the manifest. |
+ | 524 | **`modified_files_count`** | `long` | *required* | *required* |
Count of entries with status MODIFIED in the manifest. |
+ | 512 | **`added_rows_count`** | `long` | *required* | *required* | Total
number of rows in ADDED entries. |
+ | 513 | **`existing_rows_count`** | `long` | *required* | *required* |
Total number of rows in EXISTING entries. |
+ | 514 | **`deleted_rows_count`** | `long` | *required* | *required* |
Total number of rows in DELETED entries. |
+ | 521 | **`replaced_rows_count`** | `long` | *required* | *required* |
Total number of rows in REPLACED entries. |
+ | 525 | **`modified_rows_count`** | `long` | *required* | *required* |
Total number of rows in MODIFIED entries. |
+ | 516 | **`min_sequence_number`** | `long` | *required* | *required* |
Minimum data sequence number of all live entries in the manifest. |
+ | 522 | **`dv`** | `binary` | *optional* | *optional* | Roaring bitmap of
entry positions in the manifest that are not live in the current snapshot. |
+ | 523 | **`dv_cardinality`** | `long` | *optional* | *optional* |
Cardinality of the manifest deletion vector. Must be set when `dv` is non-null;
must be null otherwise. |
+
+ **`column_file` struct (element 159 of `column_files`, field 158)**
+
+ | Field id | Name | Type | Write | Read | Description |
+ |----------|------|------|-------|------|-------------|
+ | 161 | **`format_version`** | `int` | *required* | *required* | Format
version of this column file. |
+ | 162 | **`field_ids`** | `list<163: int>` | *required* | *required* |
Live field IDs stored in this column file. |
+ | 164 | **`location`** | `string` | *required* | *required* | Location of
the column file. |
+ | 165 | **`file_format`** | `string` | *required* | *required* | String
file format name: `avro`, `orc`, or `parquet`. |
+ | 166 | **`file_size_in_bytes`** | `long` | *required* | *required* |
Total column file size in bytes. |
+ | 167 | **`key_metadata`** | `binary` | *optional* | *optional* |
Implementation-specific key metadata for encryption. |
+ | 168 | **`split_offsets`** | `list<169: long>` | *optional* | *optional*
| Split offsets for the column file. Must be sorted ascending. |
+
+ When a file is added to the dataset, its content entry must set status to
ADDED (1) and store the snapshot ID in which the file was added.
Review Comment:
>How do we cover the status transitions: e.g. a file/manifest starts with
ADDED, but the next commit it flips to EXISTING (unless it got
deleted/replaced). Same for MODIFIED -> EXISTING transition.
I'm not sure if we explicitly need to call out the ADDED/MODIFIED ->
EXISTING transitions? I think the only state transitions we need to call out
are the ones where it's a net new change in a given snapshot.
If you look at the current spec (not these changes but the ones for v1-v3),
we never really needed to call out the explicit EXISTING transition because
anything that was a new change, like ADDED/DELETED had explicit mentions. After
defining those, it's very reasonably implied and via the naming of the status
EXISTING that any carry over should just be marked as EXISTING.
If we want to have EXISTING be this explicit transition I think we can do it
but we'll want to be not overly-specified to the point where we prevent certain
write patterns (more on that in the next response).
>But for files that live in leaf manifests, we don't want to rewrite
manifests for the sake of doing the status transition. For instance, if we
modified DVs on a bunch of files, we might write a new leaf manifest with a
bunch of MODIFIED entries (and the manifest status itself would have an
ADDED?), but in the next commit, the leaf status might change, but the entries
inside the leaf stays MODIFIED.
Agree, we definitley don't want to _have_ to rewrite manifests just to
update statuses, that would be a crazy bad requirement but I don't know if that
means we need to codify explicit transition rules for EXISTING in the spec. I
just worry that if we do that too strictly it may be misinterpreted and prevent
valid write scenarios.
Every additional statement we make in the spec bears the risk of
misinterpretation which is where I'm coming from that we need to be careful.
Concretely:
Status just indicates what the status of that file in the tree is (whether
it's a data file or a manifest is inconsequential)
Assume we stick with the status quo of not epxlicitly defining when to state
transition to Existing and rather it's implied that anything that's not a new
change (not ADDED/DELETED/MODIFIED/REPLACED) is EXISTING:
Both options of the following options are valid:
1/ In the scenario you described, a writer can choose to mark the leaf
manifest as EXISTING (whatever it
or
2/ A writer can choose to actually just write a new manifest with EXISTING
entries and mark the old manifest as DELETED.
Could we explicitly enumerate every single state transition or find some
wording that generalizes across use cases? Probably, but I think I'd rather
just be explicit cases where we know specific statuses are required to be
produce (like DV changes/column updates producing REPLACED + MODIFIED, file
removals explicitly producing DELETED).
That's a smaller state to enumerate and less chance of misinterpretation
preventing legitimate write scenarios. Every other status is just naturally
implied and readers/change detection should correctly handle those, unless
there's some ambiguous case we're worried about.
Let me know what you think @anoopj , cc @stevenzwu @RussellSpitzer @rdblue
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