The <source>_traverse_files functions take a callback for processing
files, but both the local and libpq source implementations called the
function directly without using the callback argument. While there is
no bug right now as the function called is the same as the callback,
fix by calling the callback to reduce the risk of subtle bugs in the
future.
Author: Junwang Zhao <zhjwpku@gmail.com>
Reviewed-by: Richard Guo <guofenglinux@gmail.com>
Discussion: https://postgr.es/m/CAEG8a3Jdwgh+PZr2zh1=t8apA4Yz8tKq+uubPqoCt14nvWKHEw@mail.gmail.com
In order to have the option to use O_DIRECT/FILE_FLAG_NO_BUFFERING in a
later commit, we need the addresses of user space buffers to be well
aligned. The exact requirements vary by OS and file system (typically
sectors and/or memory pages). The address alignment size is set to
4096, which is enough for currently known systems: it matches modern
sectors and common memory page size. There is no standard governing
O_DIRECT's requirements so we might eventually have to reconsider this
with more information from the field or future systems.
Aligning I/O buffers on memory pages is also known to improve regular
buffered I/O performance.
Three classes of I/O buffers for regular data pages are adjusted:
(1) Heap buffers are now allocated with the new palloc_aligned() or
MemoryContextAllocAligned() functions introduced by commit 439f6175.
(2) Stack buffers now use a new struct PGIOAlignedBlock to respect
PG_IO_ALIGN_SIZE, if possible with this compiler. (3) The buffer
pool is also aligned in shared memory.
WAL buffers were already aligned on XLOG_BLCKSZ. It's possible for
XLOG_BLCKSZ to be configured smaller than PG_IO_ALIGNED_SIZE and thus
for O_DIRECT WAL writes to fail to be well aligned, but that's a
pre-existing condition and will be addressed by a later commit.
BufFiles are not yet addressed (there's no current plan to use O_DIRECT
for those, but they could potentially get some incidental speedup even
in plain buffered I/O operations through better alignment).
If we can't align stack objects suitably using the compiler extensions
we know about, we disable the use of O_DIRECT by setting PG_O_DIRECT to
0. This avoids the need to consider systems that have O_DIRECT but
can't align stack objects the way we want; such systems could in theory
be supported with more work but we don't currently know of any such
machines, so it's easier to pretend there is no O_DIRECT support
instead. That's an existing and tested class of system.
Add assertions that all buffers passed into smgrread(), smgrwrite() and
smgrextend() are correctly aligned, unless PG_O_DIRECT is 0 (= stack
alignment tricks may be unavailable) or the block size has been set too
small to allow arrays of buffers to be all aligned.
Author: Thomas Munro <thomas.munro@gmail.com>
Author: Andres Freund <andres@anarazel.de>
Reviewed-by: Justin Pryzby <pryzby@telsasoft.com>
Discussion: https://postgr.es/m/CA+hUKGK1X532hYqJ_MzFWt0n1zt8trz980D79WbjwnT-yYLZpg@mail.gmail.com
The pg_fatal log which included filesizes were using UINT64_FORMAT for
the size_t variables, which failed on 32 bit buildfarm animals. Change
to using plain int instead, which is in line with how digestControlFile
is doing it already.
Per buildfarm animals florican and lapwing.
Discussion: https://postgr.es/m/13C2BF64-4A6D-47E4-9181-3A658F00C9B7@yesql.se
There's a race condition if a file changes in the source system
after we have collected the file list. If the file becomes larger,
we only fetched up to its original size. That can easily result in
a truncated file. That's not a problem for relation files, files
in pg_xact, etc. because any actions on them will be replayed from
the WAL. However, configuration files are affected.
This commit mitigates the race condition by fetching small files in
whole, even if they have grown. A test is added in which an extra
file copied is concurrently grown with the output of pg_rewind thus
guaranteeing it to have changed in size during the operation. This
is not a full fix: we still believe the original file size for files
larger than 1 MB. That should be enough for configuration files,
and doing more than that would require big changes to the chunking
logic in libpq_source.c.
This mitigates the race condition if the file is modified between
the original scan of files and copying the file, but there's still
a race condition if a file is changed while it's being copied.
That's a much smaller window, though, and pg_basebackup has the
same issue.
This race can be seen with pg_auto_failover, which frequently uses
ALTER SYSTEM, which updates postgresql.auto.conf. Often, pg_rewind
will fail, because the postgresql.auto.conf file changed concurrently
and a partial version of it was copied to the target. The partial
file would fail to parse, preventing the server from starting up.
Author: Heikki Linnakangas
Reviewed-by: Cary Huang
Discussion: https://postgr.es/m/f67feb24-5833-88cb-1020-19a4a2b83ac7%40iki.fi
This makes the abstraction of a "source" server more clear, by introducing
a common abstract class, borrowing the object-oriented programming term,
that represents all the operations that can be done on the source server.
There are two implementations of it, one for fetching via libpq, and
another to fetch from a local directory. This adds some code, but makes it
easier to understand what's going on.
The copy_executeFileMap() and libpq_executeFileMap() functions contained
basically the same logic, just calling different functions to fetch the
source files. Refactor so that the common logic is in one place, in a new
function called perform_rewind().
Reviewed-by: Kyotaro Horiguchi, Soumyadeep Chakraborty
Discussion: https://www.postgresql.org/message-id/0c5b3783-af52-3ee5-f8fa-6e794061f70d%40iki.fi
