Fix rare bug in read_stream.c's split IO handling.
The internal queue of buffers could become corrupted in a rare edge case
that failed to invalidate an entry, causing a stale buffer to be
"forwarded" to StartReadBuffers(). This is a simple fix for the
immediate problem.
A small API change might be able to remove this and related fragility
entirely, but that will have to wait a bit.
Defect in commit
ed0b87ca.
Bug: 19006
Backpatch-through: 18
Reported-by: Alexander Lakhin <exclusion@gmail.com>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Xuneng Zhou <xunengzhou@gmail.com>
Discussion: https://postgr.es/m/19006-
80fcaaf69000377e%40postgresql.org