[GitHub] [iceberg-docs] alexjo2144 commented on a diff in pull request #69: Add stats format specification

[GitBox <gi...@apache.org>]

alexjo2144 commented on code in PR #69:
URL: https://github.com/apache/iceberg-docs/pull/69#discussion_r876196718


##########
landing-page/content/common/index-and-statistics-format.md:
##########
@@ -0,0 +1,144 @@
+---
+url: index-and-statistics-format
+toc: false
+---
+<!--
+ - Licensed to the Apache Software Foundation (ASF) under one or more
+ - contributor license agreements.  See the NOTICE file distributed with
+ - this work for additional information regarding copyright ownership.
+ - The ASF licenses this file to You under the Apache License, Version 2.0
+ - (the "License"); you may not use this file except in compliance with
+ - the License.  You may obtain a copy of the License at
+ -
+ -   http://www.apache.org/licenses/LICENSE-2.0
+ -
+ - Unless required by applicable law or agreed to in writing, software
+ - distributed under the License is distributed on an "AS IS" BASIS,
+ - WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ - See the License for the specific language governing permissions and
+ - limitations under the License.
+ -->
+
+# Index and statistics file format
+
+This is a specification for the Plain Format for Iceberg Statistics, a file
+format designed to store information such as statistics about data managed in an
+Iceberg table that cannot be stored directly within the Iceberg manifest. A
+statistics file contains arbitrary pieces of information (here called "blobs"),
+along with metadata necessary to interpret them. The blobs supported by Iceberg
+are documented at [Blob types](#blob-types).
+
+## Format specification
+
+A file conforming to the format specification should have the structure as
+described below.
+
+### Versions
+
+Currently, there is a single version of the file format, described below.
+
+### File structure
+
+The file has the following structure
+
+```
+Magic Blob₁ Blob₂ ... Blobₙ Footer
+```
+
+where
+
+- `Magic` is four bytes 0x50, 0x46, 0x42, 0x31 (short for: Plain Format for
+  Blobs, version 1),
+- `Blobᵢ` is i-th blob contained in the file, to be interpreted by application
+  according to the footer,
+- `Footer` is defined below.
+
+### Footer structure
+
+Footer has the following structure
+
+```
+Magic FooterPayload FooterPayloadSize Flags Magic
+```
+
+where
+
+- `Magic`: four bytes, same as at the beginning of the file.
+- `FooterPayload`: optionally compressed, UTF-8 encoded JSON payload describing the
+  blobs in the file, with the structure described below,
+- `FooterPayloadSize`: a length in bytes of the `FooterPayload` (compressed),
+  stored as 4 byte integer,
+- `Flags`: 4 bytes for boolean flags
+  - byte 0 (first)
+    - bit 0 (lowest bit): whether `FooterPayload` is compressed
+    - all other bits are reserved for future use and should be set to 0 on write
+  - all other bytes are reserved for future use and should be set to 0 on write
+
+A 4 byte integer is always signed, in a two's complement representation, stored
+little-endian.
+
+### Footer Payload
+
+Footer payload bytes is either uncompressed or LZ4-compressed (as a single

Review Comment:
   How do you know if the data is compressed or not when reading the footer?



-- 
This is an automated message from the Apache Git Service.
To respond to the message, please log on to GitHub and use the
URL above to go to the specific comment.

To unsubscribe, e-mail: issues-unsubscribe@iceberg.apache.org

For queries about this service, please contact Infrastructure at:
users@infra.apache.org


---------------------------------------------------------------------
To unsubscribe, e-mail: issues-unsubscribe@iceberg.apache.org
For additional commands, e-mail: issues-help@iceberg.apache.org