Planner improvements

[systay]

Description

Two minor planner improvements - first a query hint that allow users to select the planner to use. Sometimes we want to be able to specify a different planner than the one the vtgate is configured with, and this query hint enables this.

select /*vt+ PLANNER=gen4 */ * from commerce;

Also re-introduces the left-to-right planner which mimics straight join on mysql, which was lost during the refactor of gen4 this week.

[systay]

@frouioui WDYT - should we use this to replace the GEN4_COMPARE_ONLY_GEN4 annotations?

[GuptaManan100]

Do we need a test for the left to right solver?

[harshit-gangal]

@frouioui WDYT - should we use this to replace the GEN4_COMPARE_ONLY_GEN4 annotations?

this would basically mean that set PLANNER=Gen4 in the comment. I think we can do that.

[harshit-gangal]

looks like we have something already GEN4_COMPARE_ONLY_V3, GEN4_COMPARE_ONLY_GEN4but those names were not intuitive to use, this looks good.

[frouioui]

@frouioui WDYT - should we use this to replace the GEN4_COMPARE_ONLY_GEN4 annotations?

Yes, that is a good idea!

[aquarapid]

Noting the valid values for the comment (/*vt+ PLANNER=xxx */):

• v3
• gen4
• gen4greedy or greedy
• left2right
• gen4fallback
• gen4comparev3

[systay]

Docs added: https://vitess.io/docs/13.0/reference/compatibility/query_planner/