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acf1dd4234
Suppress further attempts to read ahead in the WAL if we run out of
data, until the records already decoded have been replayed. This
restores the traditional behavior for continuous archive recovery, which
is to retry the failing restore_command only every 5 seconds. With the
coding in 5dc0418f, we would start retrying every time through the
recovery loop when our WAL decoding window hit the end of the current
segment and we tried to look ahead into a not-yet-available next file.
That was very slow.
Also change the no_readahead_until mechanism to use <= rather than <,
which seems more useful. Otherwise we'd either get one extra unwanted
retry of restore_command, or we'd need to add 1 to an LSN.
No change in behavior for regular streaming. That was already limited
by the flushedUpto variable, which won't be updated until we replay what
we have already.
Reported by Andres Freund while analyzing the failure of a TAP test on
build farm animal skink (investigation ongoing but probably due to
otherwise unrelated timing bugs triggered by this slowness magnified by
valgrind).
Discussion: https://postgr.es/m/20220409005910.alw46xqmmgny2sgr%40alap3.anarazel.de
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/.