几天以来，我在我的系统日志中看到了这样的消息：
Sep 23 14:28:42 server kernel: [138926.637593] php5-fpm[6455]: segfault at 7f9ade735018 ip 00007f9ae4026772 sp 00007ffd69b4fad0 error 4 in libmysqlclient.so.18.0.0[7f9ae3ff9000+2f1000]
Sep 23 14:28:44 server kernel: [138928.314016] php5-fpm[22742]: segfault at 7f9ade3db018 ip 00007f9ae4026772 sp 00007ffd69b4fad0 error 4 in libmysqlclient.so.18.0.0[7f9ae3ff9000+2f1000]
Sep 23 14:32:11 server kernel: [139135.318287] php5-fpm[16887]: segfault at 7f9ade4b3018 ip 00007f9ae4026772 sp 00007ffd69b4fad0 error 4 in libmysqlclient.so.18.0.0[7f9ae3ff9000+2f1000]
Sep 23 14:32:49 server kernel: [139173.050377] php5-fpm[668]: segfault at 7f9ade61a018 ip 00007f9ae4026772 sp 00007ffd69b4fad0 error 4 in libmysqlclient.so.18.0.0[7f9ae3ff9000+2f1000]
Sep 23 14:33:19 server kernel: [139203.396935] php5-fpm[26277]: segfault at 7f9ade6c0018 ip 00007f9ae4026772 sp 00007ffd69b4fad0 error 4 in libmysqlclient.so.18.0.0[7f9ae3ff9000+2f1000]
Sep 23 14:35:06 server kernel: [139310.048740] php5-fpm[27017]: segfault at 7f9ade46c018 ip 00007f9ae4026772 sp 00007ffd69b4fad0 error 4 in libmysqlclient.so.18.0.0[7f9ae3ff9000+2f1000]
Sep 23 14:35:19 server kernel: [139323.494188] php5-fpm[31263]: segfault at 7f9ade5e2018 ip 00007f9ae4026772 sp 00007ffd69b4fad0 error 4 in libmysqlclient.so.18.0.0[7f9ae3ff9000+2f1000]
Sep 23 14:36:10 server kernel: [139374.904308] php5-fpm[26422]: segfault at 7f9ade6cf018 ip 00007f9ae4026772 sp 00007ffd69b4fad0 error 4 in libmysqlclient.so.18.0.0[7f9ae3ff9000+2f1000]
Sep 23 14:37:25 server kernel: [139449.360384] php5-fpm[20806]: segfault at 7f9ade644018 ip 00007f9ae4026772 sp 00007ffd69b4fad0 error 4 in libmysqlclient.so.18.0.0[7f9ae3ff9000+2f1000]
我使用的是 Debian 8 和 MariaDB。一开始它每 2 或 3 小时才出现一次，但现在每小时会出现几次。经过一番研究，我明白这应该是内存问题，但我没有找到任何解决方案来解决这个问题。
这是我在 mysqltuner 中看到的内容：
-------- Storage Engine Statistics -------------------------------------------
[--] Status: +ARCHIVE +Aria +BLACKHOLE +CSV +FEDERATED +InnoDB +MRG_MyISAM
[--] Data in InnoDB tables: 2G (Tables: 79)
[--] Data in MyISAM tables: 96M (Tables: 146)
[--] Data in PERFORMANCE_SCHEMA tables: 0B (Tables: 52)
[!!] Total fragmented tables: 34
-------- Security Recommendations -------------------------------------------
[OK] All database users have passwords assigned
-------- Performance Metrics -------------------------------------------------
[--] Up for: 1d 16h 44m 38s (73M q [502.853 qps], 196K conn, TX: 572B, RX: 14B)
[--] Reads / Writes: 97% / 3%
[--] Total buffers: 17.3G global + 56.2M per thread (500 max threads)
[!!] Maximum possible memory usage: 44.8G (142% of installed RAM)
[OK] Slow queries: 0% (2K/73M)
[OK] Highest usage of available connections: 28% (141/500)
[OK] Key buffer size / total MyISAM indexes: 1.0G/32.6M
[OK] Key buffer hit rate: 100.0% (132M cached / 53K reads)
[OK] Query cache efficiency: 44.9% (50M cached / 113M selects)
[!!] Query cache prunes per day: 260596
[OK] Sorts requiring temporary tables: 0% (2K temp sorts / 2M sorts)
[OK] Temporary tables created on disk: 21% (6K on disk / 28K total)
[OK] Thread cache hit rate: 99% (141 created / 196K connections)
[OK] Table cache hit rate: 72% (500 open / 692 opened)
[OK] Open file limit used: 17% (429/2K)
[OK] Table locks acquired immediately: 99% (25M immediate / 25M locks)
[OK] InnoDB buffer pool / data size: 16.0G/2.4G
[!!] InnoDB log waits: 30
因此，要使用的最大内存太高，但我将 innodb 缓冲池大小调整为 16Go，对于 32Go RAM 应该没问题，我不知道如何优化它。
问题是，我的服务器内存总体使用率始终低于 89%（加上缓存）。MySQL 实际上使用了 50.6% 的 RAM。我不知道所有这些之间是否有联系，但我更愿意把它放在这里。否则，MySQL 方面一切似乎都很好……
最后，我调整了 my.cnf 中的以下主要变量，这些变量可能会对此产生影响：
max_connections = 100
max_heap_table_size = 64M
read_buffer_size = 4M
read_rnd_buffer_size = 32M
sort_buffer_size = 8M
query_cache_size = 256M
query_cache_limit = 4M
query_cache_type = 1
query_cache_strip_comments =1
thread_stack = 192K
transaction_isolation = READ-COMMITTED
tmp_table_size = 64M
nnodb_additional_mem_pool_size = 16M
innodb_buffer_pool_size = 16G
thread_cache_size = 4M
max_connections = 500
join_buffer_size = 12M
interactive_timeout = 30
wait_timeout = 30
open_files_limit = 800
innodb_file_per_table
key_buffer_size = 1G
table_open_cache = 500
innodb_log_file_size = 256M
两天前，服务器无缘无故崩溃了，系统日志中除了段错误之外什么都没有。段错误会导致系统崩溃吗？对段错误的原因有什么想法吗？有几种方法可以了解问题的根源？