[IGNITE-14557] Improve row layout.

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Labels: iep-54 ignite-3
• Ignite Flags: Docs Required, Release Notes Required
• Assignee: Andrey Mashenkov
• Reporter: Andrey Mashenkov
• Created: 15/Apr/21 15:01
• Updated: 19/Jul/21 09:35
• Resolved: 05/May/21 16:32

Description

Motivation.

When one try to read a column value from a row, the very first check will be a null-check.
As Null-Table resides right after an Offset-Table, the we need 2 jumps to for the null-check.

Description.

Assuming, Null-Table reserves a bit for each columns even if the columns is not Nullable,
Null-table has constant size (within same version of schema) and we no need extra bytes to persist it's length into the tuple.

• Null-checks will not require extra read for Offset-Table size and extra jump.
• Offset-Table will not need extra read/jump to reach as Null-Table size is constant.

Let's just swap these tables in layout and fix docs README.md and IEP.

 

Issue Links

• is a child of: IGNITE-13616 IEP-54 Live schema for tables
• is related to: IGNITE-14746 Improve row layout. Omit offset for the first varlen.
• links to: GitHub Pull Request #100