QbeastFormat 0.6.0

The version 0.6.0 introduces a new format for the Qbeast tables.

This document states the main changes and how we can recover a table written with a past version.

Metadata changes

• The information about the replicated cubes are not stored in the Delta log anymore.
• A physical file can contain data from multiple blocks, so the information stored in the tags of an addentry in the Delta log provides information about all the blocks stored in the corresponding index file.

Block metadata before v0.6.0

Before the version 0.6.0 the tags attribute of the add entry contained a JSON like the following:

"tags": {
  "state": "FLOODED",
  "cube": "w",
  "revision": "1",
  "minWeight": "2",
  "maxWeight": "3",
  "elementCount": "4" 
}

Term	Description
cube	The serialized representation of the Cube.
revision	The metadata of the tree.
elementCount	The number of elements in the block.
minWeight	The minimum weight of the block.
maxWeight	The maximum weight of the block.

Block metadata from v0.6.0

From the version 0.6.0 the tags attribute of the add entry contains a JSON like the following:

"tags": {
  "revision": "1",
  "blocks": "[
    {
      \"cube\": \"w\",
      \"minWeight\": 2,
      \"maxWeight\": 3,
      \"replicated\": false,
      \"elementCount\": 4
    },
    {
      \"cube\": \"wg\",
      \"minWeight\": 5,
      \"maxWeight\": 6,
      \"replicated\": false,
      \"elementCount\": 7
    },
  ]" 
}

The blocks attribute contains a string which is a JSON with necessary escapes for the quotes.

How to transform an existing table

It is possible to transform a table written with the library with the version before 0.6.0 into a table compatible with the version 0.6.0 without reindexing the table data. The utility should implement the following steps:

• remove the information about the replicated cubes from the Delta log metadata
• for each add entry in the Delta log remove all the tags except the revision tag and add the blocks tag containing the only block having the same values for the cube, minWeight, etc attributes. The replicated attribute of the block should be true if and only if the value of the state tag in the original entry is REPLICATED or ANNOUNCED

To automate the transformation it is strongly recommended to use an appropriate Delta library which allows to manipulate the Delta log, for example, in case of Scala use "io.delta" %% "delta-core" % 2.4.0 or above.