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Brown-paper-bag bug in commit 7c91a0364: when we rearranged the placement of "reltuples += 1" statements, we missed including one in this code path. The net effect of that was that CREATE INDEX CONCURRENTLY would set the table's pg_class.reltuples to zero, as would index builds done during bootstrap mode. (It seems like parallel index builds ought to fail similarly, but they don't, perhaps because reltuples is computed in some other way. You certainly couldn't figure that out from the abysmally underdocumented parallelism code in this area.) I was led to this by wondering why initdb seemed to have slowed down as a result of 7c91a0364, as is evident in the buildfarm's timing history. The reason is that every system catalog with indexes had pg_class.reltuples = 0 after bootstrap, causing the planner to make some terrible choices for queries in the post-bootstrap steps. On my workstation, this fix causes the runtime of "initdb -N" to drop from ~2.0 sec to ~1.4 sec, which is almost though not quite back to where it was in v10. That's not much of a deal for production use perhaps, but it makes a noticeable difference for buildfarm and "make check-world" runs, which do a lot of initdbs.
PostgreSQL Database Management System ===================================== This directory contains the source code distribution of the PostgreSQL database management system. PostgreSQL is an advanced object-relational database management system that supports an extended subset of the SQL standard, including transactions, foreign keys, subqueries, triggers, user-defined types and functions. This distribution also contains C language bindings. PostgreSQL has many language interfaces, many of which are listed here: https://www.postgresql.org/download See the file INSTALL for instructions on how to build and install PostgreSQL. That file also lists supported operating systems and hardware platforms and contains information regarding any other software packages that are required to build or run the PostgreSQL system. Copyright and license information can be found in the file COPYRIGHT. A comprehensive documentation set is included in this distribution; it can be read as described in the installation instructions. The latest version of this software may be obtained at https://www.postgresql.org/download/. For more information look at our web site located at https://www.postgresql.org/.