我们在 VMWare 上的 CentOS 5.5 上使用 MySQL 5.0.77：
Linux dev.ic.soschildrensvillages.org.uk 2.6.18-194.11.4.el5PAE #1 SMP Tue Sep 21 05:48:23 EDT 2010 i686 i686 i386 GNU/Linux
我们最近将内存从 4GB 升级到了 8GB。升级后，mysqldump 隔夜备份的时间从不到 10 分钟增加到了超过 2 小时。由于数据库负载过大，这也导致基于 plone 的网站无响应。转储使用优化的 mysqldump 格式，并通过套接字直接传输到另一台服务器。
任何关于我们能做什么来修复的想法都非常感谢。升级 MySQL 有帮助吗？我们可以对 MySQL 配置做些什么？我们可以对 Linux 配置做些什么？或者我们必须添加另一台服务器或转到 64 位？
我们在 6GB PAE 上运行了之前的（非虚拟）服务器，没有发现类似的问题。这是在相同的 MySQL 版本上，但是是 Centos 4.4。
服务器配置文件：
[mysqld]
port=3307
socket=/tmp/mysql_live.sock
wait_timeout=31536000
interactive_timeout=31536000
datadir=/var/mysql/live/data
user=mysql
max_connections = 200
max_allowed_packet = 64M
table_cache = 2048
binlog_cache_size = 128K
max_heap_table_size = 32M
sort_buffer_size = 2M
join_buffer_size = 2M
lower_case_table_names = 1
innodb_data_file_path = ibdata1:10M:autoextend
innodb_buffer_pool_size=1G
innodb_log_file_size=300M
innodb_log_buffer_size=8M
innodb_flush_log_at_trx_commit=1
innodb_file_per_table
[mysqldump]
# Do not buffer the whole result set in memory before writing it to
# file. Required for dumping very large tables
quick
max_allowed_packet = 64M
[mysqld_safe]
# Increase the amount of open files allowed per process. Warning: Make
# sure you have set the global system limit high enough! The high value
# is required for a large number of opened tables
open-files-limit = 8192
服务器变量：
mysql> show variables;
+---------------------------------+------------------------------------------------------------------+
| Variable_name | Value |
+---------------------------------+------------------------------------------------------------------+
| auto_increment_increment | 1 |
| auto_increment_offset | 1 |
| automatic_sp_privileges | ON |
| back_log | 50 |
| basedir | /usr/local/mysql-5.0.77-linux-i686-glibc23/ |
| binlog_cache_size | 131072 |
| bulk_insert_buffer_size | 8388608 |
| character_set_client | latin1 |
| character_set_connection | latin1 |
| character_set_database | latin1 |
| character_set_filesystem | binary |
| character_set_results | latin1 |
| character_set_server | latin1 |
| character_set_system | utf8 |
| character_sets_dir | /usr/local/mysql-5.0.77-linux-i686-glibc23/share/mysql/charsets/ |
| collation_connection | latin1_swedish_ci |
| collation_database | latin1_swedish_ci |
| collation_server | latin1_swedish_ci |
| completion_type | 0 |
| concurrent_insert | 1 |
| connect_timeout | 10 |
| datadir | /var/mysql/live/data/ |
| date_format | %Y-%m-%d |
| datetime_format | %Y-%m-%d %H:%i:%s |
| default_week_format | 0 |
| delay_key_write | ON |
| delayed_insert_limit | 100 |
| delayed_insert_timeout | 300 |
| delayed_queue_size | 1000 |
| div_precision_increment | 4 |
| keep_files_on_create | OFF |
| engine_condition_pushdown | OFF |
| expire_logs_days | 0 |
| flush | OFF |
| flush_time | 0 |
| ft_boolean_syntax | + -><()~*:""&| |
| ft_max_word_len | 84 |
| ft_min_word_len | 4 |
| ft_query_expansion_limit | 20 |
| ft_stopword_file | (built-in) |
| group_concat_max_len | 1024 |
| have_archive | YES |
| have_bdb | NO |
| have_blackhole_engine | YES |
| have_compress | YES |
| have_crypt | YES |
| have_csv | YES |
| have_dynamic_loading | YES |
| have_example_engine | NO |
| have_federated_engine | YES |
| have_geometry | YES |
| have_innodb | YES |
| have_isam | NO |
| have_merge_engine | YES |
| have_ndbcluster | DISABLED |
| have_openssl | DISABLED |
| have_ssl | DISABLED |
| have_query_cache | YES |
| have_raid | NO |
| have_rtree_keys | YES |
| have_symlink | YES |
| hostname | app.ic.soschildrensvillages.org.uk |
| init_connect | |
| init_file | |
| init_slave | |
| innodb_additional_mem_pool_size | 1048576 |
| innodb_autoextend_increment | 8 |
| innodb_buffer_pool_awe_mem_mb | 0 |
| innodb_buffer_pool_size | 1073741824 |
| innodb_checksums | ON |
| innodb_commit_concurrency | 0 |
| innodb_concurrency_tickets | 500 |
| innodb_data_file_path | ibdata1:10M:autoextend |
| innodb_data_home_dir | |
| innodb_adaptive_hash_index | ON |
| innodb_doublewrite | ON |
| innodb_fast_shutdown | 1 |
| innodb_file_io_threads | 4 |
| innodb_file_per_table | ON |
| innodb_flush_log_at_trx_commit | 1 |
| innodb_flush_method | |
| innodb_force_recovery | 0 |
| innodb_lock_wait_timeout | 50 |
| innodb_locks_unsafe_for_binlog | OFF |
| innodb_log_arch_dir | |
| innodb_log_archive | OFF |
| innodb_log_buffer_size | 8388608 |
| innodb_log_file_size | 314572800 |
| innodb_log_files_in_group | 2 |
| innodb_log_group_home_dir | ./ |
| innodb_max_dirty_pages_pct | 90 |
| innodb_max_purge_lag | 0 |
| innodb_mirrored_log_groups | 1 |
| innodb_open_files | 300 |
| innodb_rollback_on_timeout | OFF |
| innodb_support_xa | ON |
| innodb_sync_spin_loops | 20 |
| innodb_table_locks | ON |
| innodb_thread_concurrency | 8 |
| innodb_thread_sleep_delay | 10000 |
| interactive_timeout | 31536000 |
| join_buffer_size | 2097152 |
| key_buffer_size | 8384512 |
| key_cache_age_threshold | 300 |
| key_cache_block_size | 1024 |
| key_cache_division_limit | 100 |
| language | /usr/local/mysql-5.0.77-linux-i686-glibc23/share/mysql/english/ |
| large_files_support | ON |
| large_page_size | 0 |
| large_pages | OFF |
| lc_time_names | en_US |
| license | GPL |
| local_infile | ON |
| locked_in_memory | OFF |
| log | OFF |
| log_bin | OFF |
| log_bin_trust_function_creators | OFF |
| log_error | |
| log_queries_not_using_indexes | OFF |
| log_slave_updates | OFF |
| log_slow_queries | OFF |
| log_warnings | 1 |
| long_query_time | 10 |
| low_priority_updates | OFF |
| lower_case_file_system | OFF |
| lower_case_table_names | 1 |
| max_allowed_packet | 67108864 |
| max_binlog_cache_size | 4294963200 |
| max_binlog_size | 1073741824 |
| max_connect_errors | 10 |
| max_connections | 200 |
| max_delayed_threads | 20 |
| max_error_count | 64 |
| max_heap_table_size | 33554432 |
| max_insert_delayed_threads | 20 |
| max_join_size | 18446744073709551615 |
| max_length_for_sort_data | 1024 |
| max_prepared_stmt_count | 16382 |
| max_relay_log_size | 0 |
| max_seeks_for_key | 4294967295 |
| max_sort_length | 1024 |
| max_sp_recursion_depth | 0 |
| max_tmp_tables | 32 |
| max_user_connections | 0 |
| max_write_lock_count | 4294967295 |
| multi_range_count | 256 |
| myisam_data_pointer_size | 6 |
| myisam_max_sort_file_size | 2146435072 |
| myisam_recover_options | OFF |
| myisam_repair_threads | 1 |
| myisam_sort_buffer_size | 8388608 |
| myisam_stats_method | nulls_unequal |
| ndb_autoincrement_prefetch_sz | 1 |
| ndb_force_send | ON |
| ndb_use_exact_count | ON |
| ndb_use_transactions | ON |
| ndb_cache_check_time | 0 |
| ndb_connectstring | |
| net_buffer_length | 16384 |
| net_read_timeout | 30 |
| net_retry_count | 10 |
| net_write_timeout | 60 |
| new | OFF |
| old_passwords | OFF |
| open_files_limit | 8192 |
| optimizer_prune_level | 1 |
| optimizer_search_depth | 62 |
| pid_file | /var/mysql/live/mysqld.pid |
| plugin_dir | |
| port | 3307 |
| preload_buffer_size | 32768 |
| profiling | OFF |
| profiling_history_size | 15 |
| protocol_version | 10 |
| query_alloc_block_size | 8192 |
| query_cache_limit | 1048576 |
| query_cache_min_res_unit | 4096 |
| query_cache_size | 0 |
| query_cache_type | ON |
| query_cache_wlock_invalidate | OFF |
| query_prealloc_size | 8192 |
| range_alloc_block_size | 4096 |
| read_buffer_size | 131072 |
| read_only | OFF |
| read_rnd_buffer_size | 262144 |
| relay_log | |
| relay_log_index | |
| relay_log_info_file | relay-log.info |
| relay_log_purge | ON |
| relay_log_space_limit | 0 |
| rpl_recovery_rank | 0 |
| secure_auth | OFF |
| secure_file_priv | |
| server_id | 0 |
| skip_external_locking | ON |
| skip_networking | OFF |
| skip_show_database | OFF |
| slave_compressed_protocol | OFF |
| slave_load_tmpdir | /tmp/ |
| slave_net_timeout | 3600 |
| slave_skip_errors | OFF |
| slave_transaction_retries | 10 |
| slow_launch_time | 2 |
| socket | /tmp/mysql_live.sock |
| sort_buffer_size | 2097152 |
| sql_big_selects | ON |
| sql_mode | |
| sql_notes | ON |
| sql_warnings | OFF |
| ssl_ca | |
| ssl_capath | |
| ssl_cert | |
| ssl_cipher | |
| ssl_key | |
| storage_engine | MyISAM |
| sync_binlog | 0 |
| sync_frm | ON |
| system_time_zone | GMT |
| table_cache | 2048 |
| table_lock_wait_timeout | 50 |
| table_type | MyISAM |
| thread_cache_size | 0 |
| thread_stack | 196608 |
| time_format | %H:%i:%s |
| time_zone | SYSTEM |
| timed_mutexes | OFF |
| tmp_table_size | 33554432 |
| tmpdir | /tmp/ |
| transaction_alloc_block_size | 8192 |
| transaction_prealloc_size | 4096 |
| tx_isolation | REPEATABLE-READ |
| updatable_views_with_limit | YES |
| version | 5.0.77 |
| version_comment | MySQL Community Server (GPL) |
| version_compile_machine | i686 |
| version_compile_os | pc-linux-gnu |
| wait_timeout | 31536000 |
+---------------------------------+------------------------------------------------------------------+
237 rows in set (0.00 sec)
答案1
这听起来很奇怪。我不确定什么可以解决这个问题，但无论你遇到什么问题，我都建议你做几件事。
64位操作系统
Mysql 有相当多的内部 64 位数学运算。在其他条件相同的情况下，它在 64 位操作系统中运行速度总是更快。此外，如果您不辞辛劳地为服务器分配 8GB 内存，32 位 Mysql 仍然只能处理其中的 3GB。您仍可以通过为操作系统提供更多空间来缓存文件等来提高一些性能，但 Mysql 本身不会受益太多。
不要使用 OS 数据库包
尤其是如果您使用的是 Mysql 为其构建包的 disto。Mysql 的最新版本是 5.0.92。虽然我不知道有任何修复，但保持更新是一种很好的做法。Mysql 的更新速度相当快，在主要版本的生命周期中，速度和性能存在巨大差异。
如果我是你，我会启动一个新的 8GB VM 并安装 Mysql 5.0.92。不要忘记安装兼容库，否则 CentOS 会认为你没有安装任何 Mysql 库。我会从原始服务器转储并导入。设置从旧服务器到新服务器的复制，然后测试。一旦看起来不错，就切换。