| [860] | 1 | '\" t
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| 2 | .\" Title: vfs_aio_pthread
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| 3 | .\" Author: [see the "AUTHOR" section]
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| [988] | 4 | .\" Generator: DocBook XSL Stylesheets v1.78.1 <http://docbook.sf.net/>
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| [989] | 5 | .\" Date: 10/25/2016
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| [860] | 6 | .\" Manual: System Administration tools
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| [988] | 7 | .\" Source: Samba 4.4
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| [860] | 8 | .\" Language: English
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| 9 | .\"
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| [989] | 10 | .TH "VFS_AIO_PTHREAD" "8" "10/25/2016" "Samba 4\&.4" "System Administration tools"
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| [860] | 11 | .\" -----------------------------------------------------------------
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| 12 | .\" * Define some portability stuff
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| 14 | .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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| 15 | .\" http://bugs.debian.org/507673
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| 16 | .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
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| 28 | .\" * MAIN CONTENT STARTS HERE *
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| 29 | .\" -----------------------------------------------------------------
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| 30 | .SH "NAME"
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| 31 | vfs_aio_pthread \- implement async I/O in Samba vfs using a pthread pool
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| 32 | .SH "SYNOPSIS"
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| 33 | .HP \w'\ 'u
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| 34 | vfs objects = aio_pthread
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| 35 | .SH "DESCRIPTION"
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| 36 | .PP
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| 37 | This VFS module is part of the
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| 38 | \fBsamba\fR(7)
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| 39 | suite\&.
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| 40 | .PP
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| 41 | The
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| 42 | aio_pthread
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| 43 | VFS module enables asynchronous I/O for Samba on platforms which have the pthreads API available, without using the Posix AIO interface\&. Posix AIO can suffer from severe limitations\&. For example, on some Linux versions the real\-time signals that it uses are broken under heavy load\&. Other systems only allow AIO when special kernel modules are loaded or only allow a certain system\-wide amount of async requests being scheduled\&. Systems based on glibc (most Linux systems) only allow a single outstanding request per file descriptor which essentially makes Posix AIO useless on systems using the glibc implementation\&.
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| 44 | .PP
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| 45 | To work around all these limitations, the aio_pthread module was written\&. It uses a pthread pool instead of the internal Posix AIO interface to allow read and write calls to be process asynchronously\&. A pthread pool is created which expands dynamically by creating new threads as work is given to it to a maximum of 100 threads per smbd process\&. To change this limit see the "aio num threads" parameter below\&. New threads are not created if idle threads are available when a new read or write request is received, the new work is given to an existing idle thread\&. Threads terminate themselves if idle for one second\&.
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