DBA不可不知的作業系統核心引數
DBA不可不知的作業系統核心引數
作者
digoal
日期
2016-08-03
標籤
PostgreSQL , 核心引數 , Linux
背景
作業系統為了適應更多的硬體環境，許多初始的設定值，寬容度都很高。
如果不經調整，這些值可能無法適應HPC，或者硬體稍好些的環境。
無法發揮更好的硬體效能，甚至可能影響某些應用軟體的使用，特別是資料庫。
資料庫關心的OS核心引數
512GB 記憶體為例
1.
引數
fs.aio-max-nr
支援系統
CentOS 6, 7
引數解釋
aio-nr & aio-max-nr: . aio-nr is the running total of the number of events specified on the io_setup system call for all currently active aio contexts. . If aio-nr reaches aio-max-nr then io_setup will fail with EAGAIN. . Note that raising aio-max-nr does not result in the pre-allocation or re-sizing of any kernel data structures. . aio-nr & aio-max-nr: . aio-nr shows the current system-wide number of asynchronous io requests. . aio-max-nr allows you to change the maximum value aio-nr can grow to.
推薦設定
fs.aio-max-nr = 1xxxxxx . PostgreSQL, Greenplum 均未使用io_setup建立aio contexts. 無需設定。 如果Oracle資料庫，要使用aio的話，需要設定它。 設定它也沒什麼壞處，如果將來需要適應非同步IO，可以不需要重新修改這個設定。
2.
引數
fs.file-max
支援系統
CentOS 6, 7
引數解釋
file-max & file-nr: . The value in file-max denotes the maximum number of file handles that the Linux kernel will allocate. . When you get lots of error messages about running out of file handles, you might want to increase this limit. . Historically, the kernel was able to allocate file handles dynamically, but not to free them again. . The three values in file-nr denote : the number of allocated file handles , the number of allocated but unused file handles , the maximum number of file handles. . Linux 2.6 always reports 0 as the number of free file handles -- this is not an error, it just means that the number of allocated file handles exactly matches the number of used file handles. . Attempts to allocate more file descriptors than file-max are reported with printk, look for "VFS: file-max limit <number> reached".
推薦設定
fs.file-max = 7xxxxxxx . PostgreSQL 有一套自己管理的VFS，真正開啟的FD與核心管理的檔案開啟關閉有一套對映的機制，所以真實情況不需要使用那麼多的file handlers。 max_files_per_process 引數。 假設1GB記憶體支撐100個連線，每個連線開啟1000個檔案，那麼一個PG例項需要開啟10萬個檔案，一臺機器按512G記憶體來算可以跑500個PG例項，則需要5000萬個file handler。 以上設定綽綽有餘。
3.
引數
kernel.core_pattern
支援系統
CentOS 6, 7
引數解釋
core_pattern: . core_pattern is used to specify a core dumpfile pattern name. . max length 128 characters; default value is "core" . core_pattern is used as a pattern template for the output filename; certain string patterns (beginning with '%') are substituted with their actual values. . backward compatibility with core_uses_pid: If core_pattern does not include "%p" (default does not) and core_uses_pid is set, then .PID will be appended to the filename. . corename format specifiers: %<NUL> '%' is dropped %% output one '%' %p pid %P global pid (init PID namespace) %i tid %I global tid (init PID namespace) %u uid %g gid %d dump mode, matches PR_SET_DUMPABLE and /proc/sys/fs/suid_dumpable %s signal number %t UNIX time of dump %h hostname %e executable filename (may be shortened) %E executable path %<OTHER> both are dropped . If the first character of the pattern is a '|', the kernel will treat the rest of the pattern as a command to run. The core dump will be written to the standard input of that program instead of to a file.
推薦設定
kernel.core_pattern = /xxx/core_%e_%u_%t_%s.%p . 這個目錄要777的許可權，如果它是個軟鏈，則真實目錄需要777的許可權 mkdir /xxx chmod 777 /xxx 留足夠的空間
4.
引數
kernel.sem
支援系統
CentOS 6, 7
引數解釋
kernel.sem = 4096 2147483647 2147483646 512000 . 4096 每組多少訊號量 (>=17, PostgreSQL 每16個程式一組, 每組需要17個訊號量) , 2147483647 總共多少訊號量 (2^31-1 , 且大於4096*512000 ) , 2147483646 每個semop()呼叫支援多少操作 (2^31-1), 512000 多少組訊號量 (假設每GB支援100個連線, 512GB支援51200個連線, 加上其他程式, > 51200*2/16 綽綽有餘) . # sysctl -w kernel.sem="4096 2147483647 2147483646 512000" . # ipcs -s -l ------ Semaphore Limits -------- max number of arrays = 512000 max semaphores per array = 4096 max semaphores system wide = 2147483647 max ops per semop call = 2147483646 semaphore max value = 32767
推薦設定
kernel.sem = 4096 2147483647 2147483646 512000 . 4096可能能夠適合更多的場景, 所以大點無妨，關鍵是512000 arrays也夠了。
5.
引數
kernel.shmall = 107374182 kernel.shmmax = 274877906944 kernel.shmmni = 819200
支援系統
CentOS 6, 7
引數解釋
假設主機記憶體 512GB . shmmax 單個共享記憶體段最大 256GB (主機記憶體的一半，單位位元組) shmall 所有共享記憶體段加起來最大 (主機記憶體的80%，單位PAGE) shmmni 一共允許建立819200個共享記憶體段 (每個資料庫啟動需要2個共享記憶體段。 將來允許動態建立共享記憶體段，可能需求量更大) . # getconf PAGE_SIZE 4096
推薦設定
kernel.shmall = 107374182 kernel.shmmax = 274877906944 kernel.shmmni = 819200 . 9.2以及以前的版本，資料庫啟動時，對共享記憶體段的記憶體需求非常大，需要考慮以下幾點 Connections: (1800 + 270 * max_locks_per_transaction) * max_connections Autovacuum workers: (1800 + 270 * max_locks_per_transaction) * autovacuum_max_workers Prepared transactions: (770 + 270 * max_locks_per_transaction) * max_prepared_transactions Shared disk buffers: (block_size + 208) * shared_buffers WAL buffers: (wal_block_size + 8) * wal_buffers Fixed space requirements: 770 kB . 以上建議引數根據9.2以前的版本設定，後期的版本同樣適用。
6.
引數
net.core.netdev_max_backlog
支援系統
CentOS 6, 7
引數解釋
netdev_max_backlog ------------------ Maximum number of packets, queued on the INPUT side, when the interface receives packets faster than kernel can process them.
推薦設定
net.core.netdev_max_backlog=1xxxx . INPUT連結串列越長，處理耗費越大，如果用了iptables管理的話，需要加大這個值。
7.
引數
net.core.rmem_default net.core.rmem_max net.core.wmem_default net.core.wmem_max
支援系統
CentOS 6, 7
引數解釋
rmem_default ------------ The default setting of the socket receive buffer in bytes. . rmem_max -------- The maximum receive socket buffer size in bytes. . wmem_default ------------ The default setting (in bytes) of the socket send buffer. . wmem_max -------- The maximum send socket buffer size in bytes.
推薦設定
net.core.rmem_default = 262144 net.core.rmem_max = 4194304 net.core.wmem_default = 262144 net.core.wmem_max = 4194304
8.
引數
net.core.somaxconn
支援系統
CentOS 6, 7
引數解釋
somaxconn - INTEGER Limit of socket listen() backlog, known in userspace as SOMAXCONN. Defaults to 128. See also tcp_max_syn_backlog for additional tuning for TCP sockets.
推薦設定
net.core.somaxconn=4xxx
9.
引數
net.ipv4.tcp_max_syn_backlog
支援系統
CentOS 6, 7
引數解釋
tcp_max_syn_backlog - INTEGER Maximal number of remembered connection requests, which have not received an acknowledgment from connecting client. The minimal value is 128 for low memory machines, and it will increase in proportion to the memory of machine. If server suffers from overload, try increasing this number.
推薦設定
net.ipv4.tcp_max_syn_backlog=4xxx pgpool-II 使用了這個值，用於將超過num_init_child以外的連線queue。 所以這個值決定了有多少連線可以在佇列裡面等待。
10.
引數
net.ipv4.tcp_keepalive_intvl=20 net.ipv4.tcp_keepalive_probes=3 net.ipv4.tcp_keepalive_time=60
支援系統
CentOS 6, 7
引數解釋
tcp_keepalive_time - INTEGER How often TCP sends out keepalive messages when keepalive is enabled. Default: 2hours. . tcp_keepalive_probes - INTEGER How many keepalive probes TCP sends out, until it decides that the connection is broken. Default value: 9. . tcp_keepalive_intvl - INTEGER How frequently the probes are send out. Multiplied by tcp_keepalive_probes it is time to kill not responding connection, after probes started. Default value: 75sec i.e. connection will be aborted after ~11 minutes of retries.
推薦設定
net.ipv4.tcp_keepalive_intvl=20 net.ipv4.tcp_keepalive_probes=3 net.ipv4.tcp_keepalive_time=60 . 連線空閒60秒後, 每隔20秒發心跳包, 嘗試3次心跳包沒有響應，關閉連線。 從開始空閒，到關閉連線總共歷時120秒。
11.
引數
net.ipv4.tcp_mem=8388608 12582912 16777216
支援系統
CentOS 6, 7
引數解釋
tcp_mem - vector of 3 INTEGERs: min, pressure, max 單位 page min: below this number of pages TCP is not bothered about its memory appetite. . pressure: when amount of memory allocated by TCP exceeds this number of pages, TCP moderates its memory consumption and enters memory pressure mode, which is exited when memory consumption falls under "min". . max: number of pages allowed for queueing by all TCP sockets. . Defaults are calculated at boot time from amount of available memory. 64GB 記憶體，自動計算的值是這樣的 net.ipv4.tcp_mem = 1539615 2052821 3079230 . 512GB 記憶體，自動計算得到的值是這樣的 net.ipv4.tcp_mem = 49621632 66162176 99243264 . 這個引數讓作業系統啟動時自動計算，問題也不大
推薦設定
net.ipv4.tcp_mem=8388608 12582912 16777216 . 這個引數讓作業系統啟動時自動計算，問題也不大
12.
引數
net.ipv4.tcp_fin_timeout
支援系統
CentOS 6, 7
引數解釋
tcp_fin_timeout - INTEGER The length of time an orphaned (no longer referenced by any application) connection will remain in the FIN_WAIT_2 state before it is aborted at the local end. While a perfectly valid "receive only" state for an un-orphaned connection, an orphaned connection in FIN_WAIT_2 state could otherwise wait forever for the remote to close its end of the connection. Cf. tcp_max_orphans Default: 60 seconds
推薦設定
net.ipv4.tcp_fin_timeout=5 . 加快殭屍連線回收速度
13.
引數
net.ipv4.tcp_synack_retries
支援系統
CentOS 6, 7
引數解釋
tcp_synack_retries - INTEGER Number of times SYNACKs for a passive TCP connection attempt will be retransmitted. Should not be higher than 255. Default value is 5, which corresponds to 31seconds till the last retransmission with the current initial RTO of 1second. With this the final timeout for a passive TCP connection will happen after 63seconds.
推薦設定
net.ipv4.tcp_synack_retries=2 . 縮短tcp syncack超時時間
14.
引數
net.ipv4.tcp_syncookies
支援系統
CentOS 6, 7
引數解釋
tcp_syncookies - BOOLEAN Only valid when the kernel was compiled with CONFIG_SYN_COOKIES Send out syncookies when the syn backlog queue of a socket overflows. This is to prevent against the common 'SYN flood attack' Default: 1 . Note, that syncookies is fallback facility. It MUST NOT be used to help highly loaded servers to stand against legal connection rate. If you see SYN flood warnings in your logs, but investigation shows that they occur because of overload with legal connections, you should tune another parameters until this warning disappear. See: tcp_max_syn_backlog, tcp_synack_retries, tcp_abort_on_overflow. . syncookies seriously violate TCP protocol, do not allow to use TCP extensions, can result in serious degradation of some services (f.e. SMTP relaying), visible not by you, but your clients and relays, contacting you. While you see SYN flood warnings in logs not being really flooded, your server is seriously misconfigured. . If you want to test which effects syncookies have to your network connections you can set this knob to 2 to enable unconditionally generation of syncookies.
推薦設定
net.ipv4.tcp_syncookies=1 . 防止syn flood攻擊
15.
引數
net.ipv4.tcp_timestamps
支援系統
CentOS 6, 7
引數解釋
tcp_timestamps - BOOLEAN Enable timestamps as defined in RFC1323.
推薦設定
net.ipv4.tcp_timestamps=1 . tcp_timestamps 是 tcp 協議中的一個擴充套件項，透過時間戳的方式來檢測過來的包以防止 PAWS(Protect Against Wrapped Sequence numbers)，可以提高 tcp 的效能。
16.
引數
net.ipv4.tcp_tw_recycle net.ipv4.tcp_tw_reuse net.ipv4.tcp_max_tw_buckets
支援系統
CentOS 6, 7
引數解釋
tcp_tw_recycle - BOOLEAN Enable fast recycling TIME-WAIT sockets. Default value is 0. It should not be changed without advice/request of technical experts. . tcp_tw_reuse - BOOLEAN Allow to reuse TIME-WAIT sockets for new connections when it is safe from protocol viewpoint. Default value is 0. It should not be changed without advice/request of technical experts. . tcp_max_tw_buckets - INTEGER Maximal number of timewait sockets held by system simultaneously. If this number is exceeded time-wait socket is immediately destroyed and warning is printed. This limit exists only to prevent simple DoS attacks, you _must_ not lower the limit artificially, but rather increase it (probably, after increasing installed memory), if network conditions require more than default value.
推薦設定
net.ipv4.tcp_tw_recycle=0 net.ipv4.tcp_tw_reuse=1 net.ipv4.tcp_max_tw_buckets = 2xxxxx . net.ipv4.tcp_tw_recycle和net.ipv4.tcp_timestamps不建議同時開啟
17.
引數
net.ipv4.tcp_rmem net.ipv4.tcp_wmem
支援系統
CentOS 6, 7
引數解釋
tcp_wmem - vector of 3 INTEGERs: min, default, max min: Amount of memory reserved for send buffers for TCP sockets. Each TCP socket has rights to use it due to fact of its birth. Default: 1 page . default: initial size of send buffer used by TCP sockets. This value overrides net.core.wmem_default used by other protocols. It is usually lower than net.core.wmem_default. Default: 16K . max: Maximal amount of memory allowed for automatically tuned send buffers for TCP sockets. This value does not override net.core.wmem_max. Calling setsockopt() with SO_SNDBUF disables automatic tuning of that socket's send buffer size, in which case this value is ignored. Default: between 64K and 4MB, depending on RAM size. . tcp_rmem - vector of 3 INTEGERs: min, default, max min: Minimal size of receive buffer used by TCP sockets. It is guaranteed to each TCP socket, even under moderate memory pressure. Default: 1 page . default: initial size of receive buffer used by TCP sockets. This value overrides net.core.rmem_default used by other protocols. Default: 87380 bytes. This value results in window of 65535 with default setting of tcp_adv_win_scale and tcp_app_win:0 and a bit less for default tcp_app_win. See below about these variables. . max: maximal size of receive buffer allowed for automatically selected receiver buffers for TCP socket. This value does not override net.core.rmem_max. Calling setsockopt() with SO_RCVBUF disables automatic tuning of that socket's receive buffer size, in which case this value is ignored. Default: between 87380B and 6MB, depending on RAM size.
推薦設定
net.ipv4.tcp_rmem=8192 87380 16777216 net.ipv4.tcp_wmem=8192 65536 16777216 . 許多資料庫的推薦設定，提高網路效能
18.
引數
net.nf_conntrack_max net.netfilter.nf_conntrack_max
支援系統
CentOS 6
引數解釋
nf_conntrack_max - INTEGER Size of connection tracking table. Default value is nf_conntrack_buckets value * 4.
推薦設定
net.nf_conntrack_max=1xxxxxx net.netfilter.nf_conntrack_max=1xxxxxx
19.
引數
vm.dirty_background_bytes vm.dirty_expire_centisecs vm.dirty_ratio vm.dirty_writeback_centisecs
支援系統
CentOS 6, 7
引數解釋
============================================================== . dirty_background_bytes . Contains the amount of dirty memory at which the background kernel flusher threads will start writeback. . Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only one of them may be specified at a time. When one sysctl is written it is immediately taken into account to evaluate the dirty memory limits and the other appears as 0 when read. . ============================================================== . dirty_background_ratio . Contains, as a percentage of total system memory, the number of pages at which the background kernel flusher threads will start writing out dirty data. . ============================================================== . dirty_bytes . Contains the amount of dirty memory at which a process generating disk writes will itself start writeback. . Note: dirty_bytes is the counterpart of dirty_ratio. Only one of them may be specified at a time. When one sysctl is written it is immediately taken into account to evaluate the dirty memory limits and the other appears as 0 when read. . Note: the minimum value allowed for dirty_bytes is two pages (in bytes); any value lower than this limit will be ignored and the old configuration will be retained. . ============================================================== . dirty_expire_centisecs . This tunable is used to define when dirty data is old enough to be eligible for writeout by the kernel flusher threads. It is expressed in 100'ths of a second. Data which has been dirty in-memory for longer than this interval will be written out next time a flusher thread wakes up. . ============================================================== . dirty_ratio . Contains, as a percentage of total system memory, the number of pages at which a process which is generating disk writes will itself start writing out dirty data. . ============================================================== . dirty_writeback_centisecs . The kernel flusher threads will periodically wake up and write `old' data out to disk. This tunable expresses the interval between those wakeups, in 100'ths of a second. . Setting this to zero disables periodic writeback altogether. . ==============================================================
推薦設定
vm.dirty_background_bytes = 4096000000 vm.dirty_expire_centisecs = 6000 vm.dirty_ratio = 80 vm.dirty_writeback_centisecs = 50 . 減少資料庫程式刷髒頁的頻率，dirty_background_bytes根據實際IOPS能力以及記憶體大小設定
20.
引數
vm.extra_free_kbytes
支援系統
CentOS 6
引數解釋
extra_free_kbytes . This parameter tells the VM to keep extra free memory between the threshold where background reclaim (kswapd) kicks in, and the threshold where direct reclaim (by allocating processes) kicks in. . This is useful for workloads that require low latency memory allocations and have a bounded burstiness in memory allocations, for example a realtime application that receives and transmits network traffic (causing in-kernel memory allocations) with a maximum total message burst size of 200MB may need 200MB of extra free memory to avoid direct reclaim related latencies. . 目標是儘量讓後臺程式回收記憶體，比使用者程式提早多少kbytes回收，因此使用者程式可以快速分配記憶體。
推薦設定
vm.extra_free_kbytes=4xxxxxx
21.
引數
vm.min_free_kbytes
支援系統
CentOS 6, 7
引數解釋
min_free_kbytes: . This is used to force the Linux VM to keep a minimum number of kilobytes free. The VM uses this number to compute a watermark[WMARK_MIN] value for each lowmem zone in the system. Each lowmem zone gets a number of reserved free pages based proportionally on its size. . Some minimal amount of memory is needed to satisfy PF_MEMALLOC allocations; if you set this to lower than 1024KB, your system will become subtly broken, and prone to deadlock under high loads. . Setting this too high will OOM your machine instantly.
推薦設定
vm.min_free_kbytes = 2xxxxxx # vm.min_free_kbytes 建議每32G記憶體分配1G vm.min_free_kbytes . 防止在高負載時系統無響應，減少記憶體分配死鎖機率。
22.
引數
vm.mmap_min_addr
支援系統
CentOS 6, 7
引數解釋
mmap_min_addr . This file indicates the amount of address space which a user process will be restricted from mmapping. Since kernel null dereference bugs could accidentally operate based on the information in the first couple of pages of memory userspace processes should not be allowed to write to them. By default this value is set to 0 and no protections will be enforced by the security module. Setting this value to something like 64k will allow the vast majority of applications to work correctly and provide defense in depth against future potential kernel bugs.
推薦設定
vm.mmap_min_addr=6xxxx . 防止核心隱藏的BUG導致的問題
23.
引數
vm.overcommit_memory vm.overcommit_ratio
支援系統
CentOS 6, 7
引數解釋
============================================================== . overcommit_kbytes: . When overcommit_memory is set to 2, the committed address space is not permitted to exceed swap plus this amount of physical RAM. See below. . Note: overcommit_kbytes is the counterpart of overcommit_ratio. Only one of them may be specified at a time. Setting one disables the other (which then appears as 0 when read). . ============================================================== . overcommit_memory: . This value contains a flag that enables memory overcommitment. . When this flag is 0, the kernel attempts to estimate the amount of free memory left when userspace requests more memory. . When this flag is 1, the kernel pretends there is always enough memory until it actually runs out. . When this flag is 2, the kernel uses a "never overcommit" policy that attempts to prevent any overcommit of memory. Note that user_reserve_kbytes affects this policy. . This feature can be very useful because there are a lot of programs that malloc() huge amounts of memory "just-in-case" and don't use much of it. . The default value is 0. . See Documentation/vm/overcommit-accounting and security/commoncap.c::cap_vm_enough_memory() for more information. . ============================================================== . overcommit_ratio: . When overcommit_memory is set to 2, the committed address space is not permitted to exceed swap + this percentage of physical RAM. See above. . ==============================================================
推薦設定
vm.overcommit_memory = 0 vm.overcommit_ratio = 90 . vm.overcommit_memory = 0 時 vm.overcommit_ratio可以不設定
24.
引數
vm.swappiness
支援系統
CentOS 6, 7
引數解釋
swappiness . This control is used to define how aggressive the kernel will swap memory pages. Higher values will increase agressiveness, lower values decrease the amount of swap. . The default value is 60.
推薦設定
vm.swappiness = 0
25.
引數
vm.zone_reclaim_mode
支援系統
CentOS 6, 7
引數解釋
zone_reclaim_mode: . Zone_reclaim_mode allows someone to set more or less aggressive approaches to reclaim memory when a zone runs out of memory. If it is set to zero then no zone reclaim occurs. Allocations will be satisfied from other zones / nodes in the system. . This is value ORed together of . 1 = Zone reclaim on 2 = Zone reclaim writes dirty pages out 4 = Zone reclaim swaps pages . zone_reclaim_mode is disabled by default. For file servers or workloads that benefit from having their data cached, zone_reclaim_mode should be left disabled as the caching effect is likely to be more important than data locality. . zone_reclaim may be enabled if it's known that the workload is partitioned such that each partition fits within a NUMA node and that accessing remote memory would cause a measurable performance reduction. The page allocator will then reclaim easily reusable pages (those page cache pages that are currently not used) before allocating off node pages. . Allowing zone reclaim to write out pages stops processes that are writing large amounts of data from dirtying pages on other nodes. Zone reclaim will write out dirty pages if a zone fills up and so effectively throttle the process. This may decrease the performance of a single process since it cannot use all of system memory to buffer the outgoing writes anymore but it preserve the memory on other nodes so that the performance of other processes running on other nodes will not be affected. . Allowing regular swap effectively restricts allocations to the local node unless explicitly overridden by memory policies or cpuset configurations.
推薦設定
vm.zone_reclaim_mode=0 . 不使用NUMA
26.
引數
net.ipv4.ip_local_port_range
支援系統
CentOS 6, 7
引數解釋
ip_local_port_range - 2 INTEGERS Defines the local port range that is used by TCP and UDP to choose the local port. The first number is the first, the second the last local port number. The default values are 32768 and 61000 respectively. . ip_local_reserved_ports - list of comma separated ranges Specify the ports which are reserved for known third-party applications. These ports will not be used by automatic port assignments (e.g. when calling connect() or bind() with port number 0). Explicit port allocation behavior is unchanged. . The format used for both input and output is a comma separated list of ranges (e.g. "1,2-4,10-10" for ports 1, 2, 3, 4 and 10). Writing to the file will clear all previously reserved ports and update the current list with the one given in the input. . Note that ip_local_port_range and ip_local_reserved_ports settings are independent and both are considered by the kernel when determining which ports are available for automatic port assignments. . You can reserve ports which are not in the current ip_local_port_range, e.g.: . $ cat /proc/sys/net/ipv4/ip_local_port_range 32000 61000 $ cat /proc/sys/net/ipv4/ip_local_reserved_ports 8080,9148 . although this is redundant. However such a setting is useful if later the port range is changed to a value that will include the reserved ports. . Default: Empty
推薦設定
net.ipv4.ip_local_port_range=40000 65535 . 限制本地動態埠分配範圍，防止佔用監聽埠。
27.
引數
vm.nr_hugepages
支援系統
CentOS 6, 7
引數解釋
============================================================== nr_hugepages Change the minimum size of the hugepage pool. See Documentation/vm/hugetlbpage.txt ============================================================== nr_overcommit_hugepages Change the maximum size of the hugepage pool. The maximum is nr_hugepages + nr_overcommit_hugepages. See Documentation/vm/hugetlbpage.txt . The output of "cat /proc/meminfo" will include lines like: ...... HugePages_Total: vvv HugePages_Free: www HugePages_Rsvd: xxx HugePages_Surp: yyy Hugepagesize: zzz kB . where: HugePages_Total is the size of the pool of huge pages. HugePages_Free is the number of huge pages in the pool that are not yet allocated. HugePages_Rsvd is short for "reserved," and is the number of huge pages for which a commitment to allocate from the pool has been made, but no allocation has yet been made. Reserved huge pages guarantee that an application will be able to allocate a huge page from the pool of huge pages at fault time. HugePages_Surp is short for "surplus," and is the number of huge pages in the pool above the value in /proc/sys/vm/nr_hugepages. The maximum number of surplus huge pages is controlled by /proc/sys/vm/nr_overcommit_hugepages. . /proc/filesystems should also show a filesystem of type "hugetlbfs" configured in the kernel. . /proc/sys/vm/nr_hugepages indicates the current number of "persistent" huge pages in the kernel's huge page pool. "Persistent" huge pages will be returned to the huge page pool when freed by a task. A user with root privileges can dynamically allocate more or free some persistent huge pages by increasing or decreasing the value of 'nr_hugepages'.
推薦設定
如果要使用PostgreSQL的huge page，建議設定它。 大於資料庫需要的共享記憶體即可。
28.
引數
fs.nr_open
支援系統
CentOS 6, 7
引數解釋
nr_open: This denotes the maximum number of file-handles a process can allocate. Default value is 1024*1024 (1048576) which should be enough for most machines. Actual limit depends on RLIMIT_NOFILE resource limit. 它還影響security/limits.conf 的檔案控制程式碼限制，單個程式的開啟控制程式碼不能大於fs.nr_open，所以要加大檔案控制程式碼限制，首先要加大nr_open
推薦設定
對於有很多物件（表、檢視、索引、序列、物化檢視等）的PostgreSQL資料庫，建議設定為2000萬， 例如fs.nr_open=20480000
資料庫關心的資源限制
1. 透過/etc/security/limits.conf設定，或者ulimit設定
2. 透過/proc/$pid/limits檢視當前程式的設定
# - core - limits the core file size (KB) # - memlock - max locked-in-memory address space (KB) # - nofile - max number of open files 建議設定為1000萬 , 但是必須設定sysctl, fs.nr_open大於它，否則會導致系統無法登陸。 # - nproc - max number of processes 以上四個是非常關心的配置 .... # - data - max data size (KB) # - fsize - maximum filesize (KB) # - rss - max resident set size (KB) # - stack - max stack size (KB) # - cpu - max CPU time (MIN) # - as - address space limit (KB) # - maxlogins - max number of logins for this user # - maxsyslogins - max number of logins on the system # - priority - the priority to run user process with # - locks - max number of file locks the user can hold # - sigpending - max number of pending signals # - msgqueue - max memory used by POSIX message queues (bytes) # - nice - max nice priority allowed to raise to values: [-20, 19] # - rtprio - max realtime priority
資料庫關心的IO排程規則
1. 目前作業系統支援的IO排程策略包括cfq, deadline, noop 等。
/kernel-doc-xxx/Documentation/block -r--r--r-- 1 root root 674 Apr 8 16:33 00-INDEX -r--r--r-- 1 root root 55006 Apr 8 16:33 biodoc.txt -r--r--r-- 1 root root 618 Apr 8 16:33 capability.txt -r--r--r-- 1 root root 12791 Apr 8 16:33 cfq-iosched.txt -r--r--r-- 1 root root 13815 Apr 8 16:33 data-integrity.txt -r--r--r-- 1 root root 2841 Apr 8 16:33 deadline-iosched.txt -r--r--r-- 1 root root 4713 Apr 8 16:33 ioprio.txt -r--r--r-- 1 root root 2535 Apr 8 16:33 null_blk.txt -r--r--r-- 1 root root 4896 Apr 8 16:33 queue-sysfs.txt -r--r--r-- 1 root root 2075 Apr 8 16:33 request.txt -r--r--r-- 1 root root 3272 Apr 8 16:33 stat.txt -r--r--r-- 1 root root 1414 Apr 8 16:33 switching-sched.txt -r--r--r-- 1 root root 3916 Apr 8 16:33 writeback_cache_control.txt
如果你要詳細瞭解這些排程策略的規則，可以檢視WIKI或者看核心文件。
從這裡可以看到它的排程策略
cat /sys/block/vdb/queue/scheduler noop [deadline] cfq
修改
echo deadline > /sys/block/hda/queue/scheduler
或者修改啟動引數
grub.conf elevator=deadline
從很多測試結果來看，資料庫使用deadline排程，效能會更穩定一些。
來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/29497382/viewspace-2636776/，如需轉載，請註明出處，否則將追究法律責任。
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