Attached patches add an isolation test to the nbtree test module, which uses injection points. This provides thorough test coverage for nbtree backwards scans, including cases where we must recover from concurrent page splits, and page deletions by VACUUM.
The tests assume a default BLCKSZ of 8KiB. It would be difficult and likely not worth it to get the tests passing under any alternative BLCKSZ. We certainly rely on that assumption elsewhere to achieve the expected test coverage. However, this specific test goes further: it visibly fails on a non-default BLCKSZ. I think that that's probably okay, but I wanted to flag it. -- Peter Geoghegan
v1-0001-Run-nbtree-test-module-tests-under-autoconf-build.patch
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v1-0002-Add-test-coverage-for-nbtree-backwards-scans.patch
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