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6acada713a
When using the default innodb_log_buffer_size=2m, mariadb-backup --backup would spend a lot of time re-reading and re-parsing the log. For reads, it would be beneficial to memory-map the entire ib_logfile0 to the address space (typically 48 bits or 256 TiB) and read it from there, both during --backup and --prepare. We will introduce the Boolean read-only parameter innodb_log_file_mmap that will be OFF by default on most platforms, to avoid aggressive read-ahead of the entire ib_logfile0 in when only a tiny portion would be accessed. On Linux and FreeBSD the default is innodb_log_file_mmap=ON, because those platforms define a specific mmap(2) option for enabling such read-ahead and therefore it can be assumed that the default would be on-demand paging. This parameter will only have impact on the initial InnoDB startup and recovery. Any writes to the log will use regular I/O, except when the ib_logfile0 is stored in a specially configured file system that is backed by persistent memory (Linux "mount -o dax"). We also experimented with allowing writes of the ib_logfile0 via a memory mapping and decided against it. A fundamental problem would be unnecessary read-before-write in case of a major page fault, that is, when a new, not yet cached, virtual memory page in the circular ib_logfile0 is being written to. There appears to be no way to tell the operating system that we do not care about the previous contents of the page, or that the page fault handler should just zero it out. Many references to HAVE_PMEM have been replaced with references to HAVE_INNODB_MMAP. The predicate log_sys.is_pmem() has been replaced with log_sys.is_mmap() && !log_sys.is_opened(). Memory-mapped regular files differ from MAP_SYNC (PMEM) mappings in the way that an open file handle to ib_logfile0 will be retained. In both code paths, log_sys.is_mmap() will hold. Holding a file handle open will allow log_t::clear_mmap() to disable the interface with fewer operations. It should be noted that ever since commit 685d958e38b825ad9829be311f26729cccf37c46 (MDEV-14425) most 64-bit Linux platforms on our CI platforms (s390x a.k.a. IBM System Z being a notable exception) read and write /dev/shm/*/ib_logfile0 via a memory mapping, pretending that it is persistent memory (mount -o dax). So, the memory mapping based log parsing that this change is enabling by default on Linux and FreeBSD has already been extensively tested on Linux. ::log_mmap(): If a log cannot be opened as PMEM and the desired access is read-only, try to open a read-only memory mapping. xtrabackup_copy_mmap_snippet(), xtrabackup_copy_mmap_logfile(): Copy the InnoDB log in mariadb-backup --backup from a memory mapped file.
44 lines
1.0 KiB
C
44 lines
1.0 KiB
C
/* Copyright (c) 2000-2003, 2006 MySQL AB
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Use is subject to license terms
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; version 2 of the License.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1335 USA */
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#include "mysys_priv.h"
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#if defined _WIN32
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int my_getpagesize(void)
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{
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SYSTEM_INFO si;
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GetSystemInfo(&si);
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return si.dwPageSize;
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}
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#elif defined _SC_PAGESIZE
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int my_getpagesize(void)
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{
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return (int)sysconf(_SC_PAGESIZE);
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}
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#else
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/* Default implementation */
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int my_getpagesize(void)
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{
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return (int)8192;
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}
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#endif
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