[COMMITTERS] pgsql: Don’t push nextid too far forwards in recovery

Don’t push nextid too far forwards in recovery

Doing so allows various crash possibilities. Fix by avoiding
having PrescanPreparedTransactions() increment
ShmemVariableCache->nextXid when it has no 2PC files

Bug found by Jeff Janes, diagnosis and patch by Pavan Deolasee,
then patch re-designed for clarity and full accuracy by
Michael Paquier.

Reported-by: Jeff Janes
Author: Pavan Deolasee, Michael Paquier
Discussion: https://postgr.es/m/CAMkU=1zMLnH_i1-PVQ-biZzvNx7VcuatriquEnh7HNk6K8Ss3Q@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/aa203e76004daaee3d70b19cc727ed17b87b3d3a

Modified Files
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src/backend/access/transam/twophase.c | 77 ++++++++++++++++-------------------
1 file changed, 36 insertions(+), 41 deletions(-)