数据库_WARNING:Could not increase the asynch I/O limit to 64 for SQL direct I/O. It is set to 0_软件世界网
WARNING:Could not increase the asynch I/O limit to 64 for SQL direct I/O. It is set to 0
& 今天是，解决一下hp-unix异步Ｉ／Ｏ问题。
从trace日志中看：
WARNING:Could not increase the asynch I/O limit to 32 for SQL direct I/O. It is set to 0
WARNING:Could not increase the asynch I/O limit to 64 for SQL direct I/O. It is set to 0
WARNING:Could not increase the asynch I/O limit to 64 for SQL direct I/O. It is set to 0
WARNING:Could not increase the asynch I/O limit to 96 for SQL direct I/O. It is set to 0
WARNING:Could not increase the asynch I/O limit to 64 for SQL direct I/O. It is set to 0
WARNING:Could not increase the asynch I/O limit to 96 for SQL direct I/O. It is set to 0
09:18:51.911
WARNING:Could not increase the asynch I/O limit to 64 for SQL direct I/O. It is set to 0
WARNING:Could not increase the asynch I/O limit to 96 for SQL direct I/O. It is set to 0
WARNING:Could not increase the asynch I/O limit to 128 for SQL direct I/O. It is set to 0
09:19:03.482
WARNING:Could not increase the asynch I/O limit to 64 for SQL direct I/O. It is set to 0
WARNING:Could not increase the asynch I/O limit to 128 for SQL direct I/O. It is set to 0
可以看到是数据库异步I/0出现问题。问题排查有两个方面，数据库方面和主机方面：
第一：排查数据库：
主要有如下参数：
filesystemio_options=asynch
&disk_asynch_io=TRUE
&tape_asynch_io=TRUE
&dbwr_io_slaves=0
&backup_tape_io_slaves=FALSE
经过排查参数设置没有问题。
第二：主机侧问题。
因为机器是hp-unix，需要关注如下参数：
The following kernel parameters are used for managing asynchronous I/O operations. The first four are related to POSIX asynchronous I/O the last pertains to open ports between processes and the asynchronous disk-I/O driver:
aio_listio_max
Specifies how many POSIX asynchronous I/O operations are allowed in a single listio() call.
aio_max_ops
System-wide maximum number of POSIX asynchronous I/O operations that are allowed at any given time.
aio_physmem_pct
Maximum total system memory that can be locked for use in POSIX asynchronous I/O operations.
aio_prio_delta_max
Maximum priority offset allowed in a POSIX asynchronous I/O control block (aiocb).
max_async_ports
Maximum number of ports to the asynchronous disk-I/O driver that processes can have open at any given time.
另外主机检查是否已经配置了异步i/0参考官网文档：
/cd/B19306_01/server.102/b15658/appb_hpux.htm#i637036
& 但是在本例中看出，已经启动了部分进程的异步I/O。但是只有50个。
orarep@pmsdb2[/dev]$/usr/sbin/fuser /dev/async
/dev/async:&&& 18635o&& 11336o&& 11376o&&& 8833o&& 18637o&&& 4527o&&& 5834o&& 10723o&& 18643o&&& 7740o&&& 5751o&& 18647o&& 11330o&& 11348o&& 11370o&& 18639o&&& 2486o&& 11354o&&& 7738o&& 11391o&& 11346o&&& 5795o&& 11334o&& 10719o&& 11389o&&& 5867o&& 10721o&&
11356o&&& 8835o&&& 5749o&& 12291o&&&& 390o&&& 3617o&& 11352o&& 11344o&& 11340o&& 18645o&& 11338o&& 11342o&&& 4029o&& 11372o&& 11350o&& 11358o&&& 5785o&& 11328o&& 11332o&&&& 388o&&& 5779o
orarep@pmsdb2[/dev]$ps& -ef | grep ora_dbw3_repdb
& orarep 11340&&&& 1& 0 12?? 31& ?&&&&&&&& 2:13 ora_dbw3_repdb
& orarep& 6010&& 170& 3 09:49:44 pts/6&&&& 0:00 grep ora_dbw3_repdb
orarep@pmsdb2[/dev]$
进一步确认max_async_ports 内核参数：如下：
Description
max_async_ports limits the total number of open ports to the ansynchronous disk-I/O driver that processes on the system can have at any given time (this has nothing to do with any RS-232 asynchronous data-communications interfaces). The system allocates an
array of port structures for each port when it is opened that is used for all communication between the process and the asynchronous disk driver. The number of asynchronous ports required by a given application is usually specified in the documentation for
that application (such as database applications software, video management software, etc.).
To determine a suitable value for max_async_ports:
Determine how many ports are required for each application and/or process that uses asynchronous disk I/O.
Determine which of these applications will be running simultaneously as separate processes. Also determine whether multiple copies of an application will be running at the same time as separate processes.
Based on these numbers, determine the maximum number of open ports to the asynchronous disk driver that will be needed by all processes any given time to obtain a reasonable total.
Set max_async_ports to a value that is not less than this number.
查看该内核参数：
orarep@pmsdb2[/dev]$/usr/sbin/kctune max_async_ports
Tunable&&&&&&&&& Value& Expression&
max_async_ports&&&& 50& Default&&&&
orarep@pmsdb2[/dev]$
问题可以看出来，在系统高并发下只有50个异步进程。因此需要调整 该值为实际最大process值。
&另外有ｂｕｇ也会出现这种问题：Bug & &WARNING:Could not increase the asynch I/O limit ...& messages in trace file
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3.2Objectives；Priortotakingthisexam,ca；VDCA410Section1CImplemen；Objective1.1CImplementan；?IdentifyRAIDlevels；?IdentifysupportedHBAtyp；?Identifyvirtualdiskform；?ProductDocumentation
3.2 Objectives Prior to taking this exam, candidates should understand each of the following objectives.
Each objec along with related tools the candidate should have experience with, and related documentation that contains information relevant to the objective.
All objectives may also be referenced in other product documentation not specifically highlighted below.
The candidate should be familiar with all relevant product documentation or have an equivalent skillset. VDCA410 Section 1 C Implement and Manage Storage Objective 1.1 C Implement and Manage Complex Storage Solutions ? Identify RAID levels? Identify supported HBA types? Identify virtual disk format types ??????????????????
Product Documentation vSphere
Client vscsiStats vSphere CLIo vicfg-*Determine use cases for and configure VMware DirectPath I/O Determine requirements for and configure NPIV Determine appropriate RAID level for various Virtual Machine workloads Apply VMware storage best practices Understand use cases for Raw Device Mapping Configure vCenter Server storage filters Understand and apply VMFS resignaturing Understand and apply LUN masking using PSA-related commands Analyze I/O workloads to determine storage performance requirementso vifso vmkfstoolso esxtop/resxtop Objective 1.2 C Manage Storage Capacity in a vSphere Environment ? Identify storage provisioning methods? Identify available storage monitoring tools, metrics and alarms ?????? Apply space utilization data to manage storage resources
Provision and manage storage resources according to Virtual Machine requirements Understand interactions between virtual storage provisioning and physical storage provisioning Apply VMware storage best practices Configure datastore alarms Analyze datastore alarms and errors to determine space availability ??????? Objective 1.3 C Configure and Manage Complex Multipathing and PSA Plug-ins ? Explain the Pluggable Storage Architecture (PSA) layout ?????Install and Configure PSA plug-ins Understand different multipathing policy functionalities Perform command line configuration of multipathing options Change a multipath policy Configure Software iSCSI port binding
Product Documentation vSphere Client vSphere CLI o vmkfstools???????? Section 2 C Implement and Manage Networking Objective 2.1 C Implement and Manage Complex Virtual Networks ? Identify common virtual switch configurations ? Determine use cases for and apply IPv6? Configure NetQueue? Configure SNMP? Determine use cases for and apply VMware DirectPath I/O? Migrate a vSS network to a Hybrid or Full vDS solution? Configure vSS and vDS settings using command line tools ? Analyze command line output to identify vSS and vDS configuration details ??????? Product Documentation vSphere Client vSphere CLI o vicfg-*
Product Documentation vSphere Client vSphere CLI o esxcliObjective 2.2 C Configure and Maintain VLANs, PVLANs and VLAN Settings ? Identify types of VLANs and PVLANs ? Determine use cases for and configure VLAN Trunking? Determine use cases for and configure PVLANs? Use command line tools to troubleshoot and identify VLAN configurations?????? Objective 2.3 C Deploy and Maintain Scalable Virtual Networking ? Identify VMware NIC Teaming policies? Identify common network protocols ?????????
Product Documentation vSphere ClientUnderstand the NIC Teaming failover types and related physical network settings Determine and apply Failover settings Configure explicit failover to conform with VMware best practices Configure port groups to properly isolate network traffic
Product Documentation vSphere Client vSphere CLI o vicfg-*? vSphere CLIo vicfg-* Objective 2.4 C
Administer vNetwork Distributed Switch Settings ? Explain relationship between vDS and logical vSSes ? Understand the use of command line tools to configure appropriate vDS settings on an ESX/ESXihost? Determine use cases for and apply Port Binding settings? Configure Live Port Moving? Given a set of network requirements, identify the appropriate distributed switch technology touse? Use command line tools to troubleshoot and identify configuration items from an existing vDS?????? Section 3 C Deploy DRS Clusters and Manage Performance Objective 3.1 C Tune and Optimize vSphere Performance ? Identify appropriate BIOS and firmware setting requirements for optimal ESX/ESXi Hostperformance? Identify appropriate ESX driver revisions required for optimal ESX/ESXi Host performance? Recall where to locate information resources to verify compliance with VMware and third partyvendor best practices Product Documentation vSphere Client vSphere CLI o vicfg-*包含各类专业文献、生活休闲娱乐、专业论文、中学教育、各类资格考试、应用写作文书、幼儿教育、小学教育、95VCAPDCA_Exam_Blueprint_Guide_1.5等内容。　
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赞助商链接4.7. Direct I/O
4.7. Direct I/O
4.7. Direct I/O
Direct I/O is a feature of the file system whereby file reads and writes go directly from the applications to the storage device, bypassing the operating system read and write caches. Direct I/O is used only by applications (such as databases) that manage their own caches.
An application invokes direct I/O by opening a file with the O_DIRECT flag. Alternatively, GFS can attach a direct I/O attribute to a file, in which case direct I/O is used regardless of how the file is opened.
When a file is opened with O_DIRECT, or when a GFS direct I/O attribute is attached to a file, all I/O operations must be done in block-size multiples of 512 bytes. The memory being read from or written to must also be 512-byte aligned.
One of the following methods can be used to enable direct I/O on a file:
GFS file attribute
GFS directory attribute
Note: This documentation is provided {and copyrighted} by Red Hat(R), Inc. and is released via the Open Publication License. The copyright holder has added the further requirement that Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder. The CentOS project redistributes these original works (in their unmodified form) as a reference for CentOS-5 because CentOS-5 is built from publicly available, open source SRPMS. The documentation is unmodified to be compliant with upstream distribution policy. Neither CentOS-5 nor the CentOS Project are in any way affiliated with or sponsored by Red Hat(R), Inc.