[columnar] Fix corruption possibilities for vacuum UDF

[JerrySievert]

this should fix #169.

there are two parts to the vacuum UDF:

• combining stripes with deleted data
• moving stripes into the new holes

bailing out in the combination process is not an issue, but bailing out during the reorganization is. if we exit cleanly from the signal handlers, instead of calling the signal after we feel we are safe, we do not have corruption. unfortunately, not calling the signal that we blocked is not an acceptable solution.

interestingly, finishing a single reorganization does not corrupt, even if the signal handlers are called. this PR sets up the vacuum UDF to do a singular reorganization, renames the UDF to columnar._vacuum_internal, and creates a new columnar.vacuum that recreates the original functionality by continually calling the columnar._vacuum_internal either until done, or we reach the optional count.

this does add additional time to the UDF.

note that this does increase the version of columnar, so we will need to upgrade the extension to fully fix the problem.

[JerrySievert]

I've also added elog statements at DEBUG3 which announce state transitions, so it should be fairly easy to test if you set your statement level to DEBUG3 and cancel/terminate after beginning reorganization.

[mkaruza]

lgtm

[muntdan]

note that this does increase the version of columnar, so we will need to upgrade the extension to fully fix the problem.

This means a new Tag/version will be published for this ?

[wuputah]

every commit to main (well, any commit modifies code) has a build and tag. See:
https://github.com/hydradatabase/hydra/pkgs/container/hydra

I do plan on publishing a 1.0.2 release soon, but would be grateful for any testing you could do with the current build.

[muntdan]

So the “upgrade the extension" is included in the latest docker build?

[wuputah]

This means you need to run ALTER EXTENSION columnar UPDATE; on all existing databases using columnar after upgrading to the new build.

(This is done automatically whenever we update the columnar build on Hydra Cloud, but not done automatically for Hydra's open source image.)