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-rw-r--r--lib/kernel/doc/src/logger_chapter.xml263
-rw-r--r--lib/kernel/doc/src/logger_disk_log_h.xml134
-rw-r--r--lib/kernel/doc/src/logger_std_h.xml104
3 files changed, 263 insertions, 238 deletions
diff --git a/lib/kernel/doc/src/logger_chapter.xml b/lib/kernel/doc/src/logger_chapter.xml
index f7df0a3e6e..a4951022bb 100644
--- a/lib/kernel/doc/src/logger_chapter.xml
+++ b/lib/kernel/doc/src/logger_chapter.xml
@@ -97,6 +97,7 @@
defined.</p>
</section>
<section>
+ <marker id="logger_api"/>
<title>Logger API</title>
<p>The API for logging consists of a set
of <seealso marker="logger#macros">macros</seealso>, and a set
@@ -1103,184 +1104,210 @@ do_log(Fd, LogEvent, #{formatter := {FModule, FConfig}}) ->
<section>
<marker id="overload_protection"/>
<title>Protecting the Handler from Overload</title>
- <p>In order for the built-in handlers to survive, and stay responsive,
- during periods of high load (i.e. when huge numbers of incoming
- log requests must be handled), a mechanism for overload protection
- has been implemented in the
- <seealso marker="logger_std_h"><c>logger_std_h</c></seealso>
- and <seealso marker="logger_disk_log_h"><c>logger_disk_log_h</c>
- </seealso> handler. The mechanism, used by both handlers, works
- as follows:</p>
+ <p>The default handlers, <seealso marker="logger_std_h">
+ <c>logger_std_h</c></seealso> and <seealso marker="logger_disk_log_h">
+ <c>logger_disk_log_h</c></seealso>, feature an overload protection
+ mechanism, which makes it possible for the handlers to survive,
+ and stay responsive, during periods of high load (when huge
+ numbers of incoming log requests must be handled).
+ The mechanism works as follows:</p>
<section>
<title>Message Queue Length</title>
<p>The handler process keeps track of the length of its message
- queue and reacts in different ways depending on the current status.
- The purpose is to keep the handler in, or (as quickly as possible),
- get the handler into, a state where it can keep up with the pace
- of incoming log requests. The memory usage of the handler must never
- keep growing larger and larger, since that would eventually cause the
- handler to crash. Three thresholds with associated actions have been
- defined:</p>
+ queue and takes some form of action when the current length exceeds a
+ configurable threshold. The purpose is to keep the handler in, or to
+ as quickly as possible get the handler into, a state where it can
+ keep up with the pace of incoming log events. The memory use of the
+ handler must never grow larger and larger, since that will eventually
+ cause the handler to crash. These three thresholds, with associated
+ actions, exist:</p>
<taglist>
- <tag><c>toggle_sync_qlen</c></tag>
+ <tag><c>sync_mode_qlen</c></tag>
<item>
- <p>The default value of this level is <c>10</c> messages,
- and as long as the length of the message queue is lower, all log
- requests are handled asynchronously. This simply means that the
- process sending the log request (by calling a log function in the
- Logger API) does not wait for a response from the handler but
- continues executing immediately after the request (i.e. it will not
- be affected by the time it takes the handler to print to the log
- device). If the message queue grows larger than this value, however,
- the handler starts handling the log requests synchronously instead,
- meaning the process sending the request will have to wait for a
- response. When the handler manages to reduce the message queue to a
- level below the <c>toggle_sync_qlen</c> threshold, asynchronous
+ <p>As long as the length of the message queue is lower than this
+ value, all log events are handled asynchronously. This means that
+ the client process sending the log event, by calling a log function
+ in the <seealso marker="logger_chapter#logger_api">Logger API</seealso>,
+ does not wait for a response from the handler but continues
+ executing immediately after the event is sent. It is not affected
+ by the time it takes the handler to print the event to the log
+ device. If the message queue grows larger than this value,
+ the handler starts handling log events synchronously instead,
+ meaning that the client process sending the event must wait for a
+ response. When the handler reduces the message queue to a
+ level below the <c>sync_mode_qlen</c> threshold, asynchronous
operation is resumed. The switch from asynchronous to synchronous
- mode will force the logging tempo of few busy senders to slow down,
- but cannot protect the handler sufficiently in situations of many
- concurrent senders.</p>
+ mode can slow down the logging tempo of one, or a few, busy senders,
+ but cannot protect the handler sufficiently in a situation of many
+ busy concurrent senders.</p>
+ <p>Defaults to <c>10</c> messages.</p>
</item>
- <tag><c>drop_new_reqs_qlen</c></tag>
+ <tag><c>drop_mode_qlen</c></tag>
<item>
- <p>When the message queue has grown larger than this threshold, which
- defaults to <c>200</c> messages, the handler switches to a mode in
- which it drops any new requests being made. Dropping a message in
- this state means that the log function never actually sends a message
- to the handler. The log call simply returns without an action. When
- the length of the message queue has been reduced to a level below this
- threshold, synchronous or asynchronous request handling mode is
- resumed.</p>
+ <p>When the message queue grows larger than this threshold, the
+ handler switches to a mode in which it drops all new events that
+ senders want to log. Dropping an event in this mode means that the
+ call to the log function never results in a message being sent to
+ the handler, but the function returns without taking any action.
+ The handler keeps logging the events that are already in its message
+ queue, and when the length of the message queue is reduced to a level
+ below the threshold, synchronous or asynchronous mode is resumed.
+ Notice that when the handler activates or deactivates drop mode,
+ information about it is printed in the log.</p>
+ <p>Defaults to <c>200</c> messages.</p>
</item>
- <tag><c>flush_reqs_qlen</c></tag>
+ <tag><c>flush_qlen</c></tag>
<item>
- <p>Above this threshold, which defaults to <c>1000</c> messages, a
- flush operation takes place, in which all messages buffered in the
- process mailbox get deleted without any logging actually taking
- place. (Processes waiting for a response from a synchronous log request
- will receive a reply indicating that the request has been dropped).</p>
+ <p>If the length of the message queue grows larger than this threshold,
+ a flush (delete) operation takes place. To flush events, the handler
+ discards the messages in the message queue by receiving them in a
+ loop without logging. Client processes waiting for a response from a
+ synchronous log request receive a reply from the handler indicating
+ that the request is dropped. The handler process increases its
+ priority during the flush loop to make sure that no new events
+ are received during the operation. Notice that after the flush operation
+ is performed, the handler prints information in the log about how many
+ events have been deleted.</p>
+ <p>Defaults to <c>1000</c> messages.</p>
</item>
</taglist>
<p>For the overload protection algorithm to work properly, it is
required that:</p>
- <p><c>toggle_sync_qlen =&lt; drop_new_reqs_qlen =&lt; flush_reqs_qlen</c></p>
+ <p><c>sync_mode_qlen =&lt; drop_mode_qlen =&lt; flush_qlen</c></p>
<p>and that:</p>
- <p><c>drop_new_reqs_qlen &gt; 1</c></p>
+ <p><c>drop_mode_qlen &gt; 1</c></p>
- <p>If <c>toggle_sync_qlen</c> is set to <c>0</c>, the handler will handle all
- requests synchronously. Setting the value of <c>toggle_sync_qlen</c> to the same
- as <c>drop_new_reqs_qlen</c>, disables the synchronous mode. Likewise, setting
- the value of <c>drop_new_reqs_qlen</c> to the same as <c>flush_reqs_qlen</c>,
- disables the drop mode.</p>
+ <p>To disable certain modes, do the following:</p>
+ <list>
+ <item>If <c>sync_mode_qlen</c> is set to <c>0</c>, all log events are handled
+ synchronously. That is, asynchronous logging is disabled.</item>
+ <item>If <c>sync_mode_qlen</c> is set to the same value as
+ <c>drop_mode_qlen</c>, synchronous mode is disabled. That is, the handler
+ always runs in asynchronous mode, unless dropping or flushing is invoked.</item>
+ <item>If <c>drop_mode_qlen</c> is set to the same value as <c>flush_qlen</c>,
+ drop mode is disabled and can never occur.</item>
+ </list>
<p>During high load scenarios, the length of the handler message queue
rarely grows in a linear and predictable way. Instead, whenever the
- handler process gets scheduled in, it can have an almost arbitrary number
- of messages waiting in the mailbox. It's for this reason that the overload
- protection mechanism is focused on acting quickly and quite drastically
- (such as immediately dropping or flushing messages) as soon as a large
- queue length is detected. </p>
-
- <p>The thresholds listed above may be modified by the user if, e.g, a handler
- shouldn't drop or flush messages unless the message queue length grows
- extremely large. (The handler must be allowed to use large amounts of memory
- under such circumstances however). Another example of when the user might want
- to change the settings is if, for performance reasons, the logging processes must
- never get blocked by synchronous log requests, while dropping or flushing requests
- is perfectly acceptable (since it doesn't affect the performance of the
- loggers).</p>
+ handler process is scheduled in, it can have an almost arbitrary number
+ of messages waiting in the message queue. It is for this reason that the overload
+ protection mechanism is focused on acting quickly, and quite drastically,
+ such as immediately dropping or flushing messages, when a large queue length
+ is detected.</p>
+
+ <p>The values of the previously listed thresholds can be specified by the user.
+ This way, a handler can be configured to, for example, not drop or flush
+ messages unless the message queue length of the handler process grows extremely
+ large. Notice that large amounts of memory can be required for the node under such
+ circumstances. Another example of user configuration is when, for performance
+ reasons, the client processes must never be blocked by synchronous log requests.
+ It is possible, perhaps, that dropping or flushing events is still acceptable, since
+ it does not affect the performance of the client processes sending the log events.</p>
<p>A configuration example:</p>
<code type="none">
logger:add_handler(my_standard_h, logger_std_h,
- #{config =>
- #{type => {file,"./system_info.log"},
- toggle_sync_qlen => 100,
- drop_new_reqs_qlen => 1000,
- flush_reqs_qlen => 2000}}).
+ #{config => #{type => {file,"./system_info.log"},
+ sync_mode_qlen => 100,
+ drop_mode_qlen => 1000,
+ flush_qlen => 2000}}).
</code>
</section>
<section>
<title>Controlling Bursts of Log Requests</title>
- <p>A potential problem with large bursts of log requests, is that log files
- may get full or wrapped too quickly (in the latter case overwriting
- previously logged data that could be of great importance). For this reason,
- both built-in handlers offer the possibility to set a maximum level of how
- many requests to process with a certain time frame. With this burst control
- feature enabled, the handler will take care of bursts of log requests
- without choking log files, or the terminal, with massive amounts of
- printouts. These are the configuration parameters:</p>
-
+ <p>Large bursts of log events - many events received by the handler
+ under a short period of time - can potentially cause problems, such as:</p>
+ <list>
+ <item>Log files grow very large, very quickly.</item>
+ <item>Circular logs wrap too quickly so that important data is overwritten.</item>
+ <item>Write buffers grow large, which slows down file sync operations.</item>
+ </list>
+
+ <p>For this reason, both built-in handlers offer the possibility to specify the
+ maximum number of events to be handled within a certain time frame.
+ With this burst control feature enabled, the handler can avoid choking the log with
+ massive amounts of printouts. The configuration parameters are:</p>
<taglist>
- <tag><c>enable_burst_limit</c></tag>
+ <tag><c>burst_limit_enable</c></tag>
<item>
- <p>This is set to <c>true</c> by default. The value <c>false</c>
- disables the burst control feature.</p>
+ <p>Value <c>true</c> enables burst control and <c>false</c> disables it.</p>
+ <p>Defaults to <c>true</c>.</p>
</item>
- <tag><c>burst_limit_size</c></tag>
+ <tag><c>burst_limit_max_count</c></tag>
<item>
- <p>This is how many requests should be processed within the
- <c>burst_window_time</c> time frame. After this maximum has been
- reached, successive requests will be dropped until the end of the
- time frame. The default value is <c>500</c> messages.</p>
+ <p>This is the maximum number of events to handle within a
+ <c>burst_limit_window_time</c> time frame. After the limit is
+ reached, successive events are dropped until the end of the time frame.</p>
+ <p>Defaults to <c>500</c> events.</p>
</item>
- <tag><c>burst_window_time</c></tag>
+ <tag><c>burst_limit_window_time</c></tag>
<item>
- <p>The default window is <c>1000</c> milliseconds long.</p>
+ <p>See the previous description of <c>burst_limit_max_count</c>.</p>
+ <p>Defaults to <c>1000</c> milliseconds.</p>
</item>
</taglist>
<p>A configuration example:</p>
<code type="none">
logger:add_handler(my_disk_log_h, logger_disk_log_h,
- #{disk_log_opts =>
- #{file => "./my_disk_log"},
- config =>
- #{burst_limit_size => 10,
- burst_window_time => 500}}).
+ #{config => #{file => "./my_disk_log",
+ burst_limit_enable => true,
+ burst_limit_max_count => 20,
+ burst_limit_window_time => 500}}).
</code>
</section>
<section>
- <title>Terminating a Large Handler</title>
- <p>A handler process may grow large even if it can manage peaks of high load
- without crashing. The overload protection mechanism includes user configurable
- levels for a maximum allowed message queue length and maximum allowed memory
- usage. This feature is disabled by default, but can be switched on by means
- of the following configuration parameters:</p>
-
+ <title>Terminating an Overloaded Handler</title>
+ <p>It is possible that a handler, even if it can successfully manage peaks
+ of high load without crashing, can build up a large message queue, or use a
+ large amount of memory. The overload protection mechanism includes an
+ automatic termination and restart feature for the purpose of guaranteeing
+ that a handler does not grow out of bounds. The feature is configured
+ with the following parameters:</p>
<taglist>
- <tag><c>enable_kill_overloaded</c></tag>
+ <tag><c>overload_kill_enable</c></tag>
<item>
- <p>This is set to <c>false</c> by default. The value <c>true</c>
- enables the feature.</p>
+ <p>Value <c>true</c> enables the feature and <c>false</c> disables it.</p>
+ <p>Defaults to <c>false</c>.</p>
</item>
- <tag><c>handler_overloaded_qlen</c></tag>
+ <tag><c>overload_kill_qlen</c></tag>
<item>
- <p>This is the maximum allowed queue length. If the mailbox grows larger
- than this, the handler process gets terminated.</p>
+ <p>This is the maximum allowed queue length. If the message queue grows
+ larger than this, the handler process is terminated.</p>
+ <p>Defaults to <c>20000</c> messages.</p>
</item>
- <tag><c>handler_overloaded_mem</c></tag>
+ <tag><c>overload_kill_mem_size</c></tag>
<item>
- <p>This is the maximum allowed memory usage of the handler process. If
- the handler grows any larger, the process gets terminated.</p>
+ <p>This is the maximum memory size that the handler process is allowed to use.
+ If the handler grows larger than this, the process is terminated.</p>
+ <p>Defaults to <c>3000000</c> bytes.</p>
</item>
- <tag><c>handler_restart_after</c></tag>
+ <tag><c>overload_kill_restart_after</c></tag>
<item>
- <p>If the handler gets terminated because of its queue length or
- memory usage, it can get automatically restarted again after a
- configurable delay time. The time is specified in milliseconds
- and <c>5000</c> is the default value. The value <c>never</c> can
- also be set, which prevents a restart.</p>
+ <p>If the handler is terminated, it restarts automatically after a
+ delay specified in milliseconds. The value <c>infinity</c> prevents
+ restarts.</p>
+ <p>Defaults to <c>5000</c> milliseconds.</p>
</item>
</taglist>
+ <p>If the handler process is terminated because of overload, it prints
+ information about it in the log. It also prints information about when a
+ restart has taken place, and the handler is back in action.</p>
+ <note>
+ <p>The sizes of the log events affect the memory needs of the handler.
+ For information about how to limit the size of log events, see the
+ <seealso marker="logger_formatter"><c>logger_formatter(3)</c></seealso>
+ manual page.</p>
+ </note>
</section>
</section>
diff --git a/lib/kernel/doc/src/logger_disk_log_h.xml b/lib/kernel/doc/src/logger_disk_log_h.xml
index 63c29cb010..98439983cf 100644
--- a/lib/kernel/doc/src/logger_disk_log_h.xml
+++ b/lib/kernel/doc/src/logger_disk_log_h.xml
@@ -33,106 +33,112 @@
<file>logger_disk_log_h.xml</file>
</header>
<module>logger_disk_log_h</module>
- <modulesummary>A disk_log based handler for the Logger.</modulesummary>
+ <modulesummary>A disk_log based handler for Logger</modulesummary>
<description>
<p>This is a handler for Logger that offers circular
(wrapped) logs by using <seealso marker="disk_log"><c>disk_log</c></seealso>.
- Multiple instances
- of this handler can be added to Logger, and each instance prints to
- its own disk_log file, created with the name and settings specified in
- the handler configuration.</p>
+ Multiple instances of this handler can be added to Logger, and each instance
+ prints to its own disk log file, created with the name and settings specified
+ in the handler configuration.</p>
<p>The default standard handler,
<seealso marker="logger_std_h"><c>logger_std_h</c></seealso>, can be
- replaced by a disk_log handler at start up of the Kernel application.
+ replaced by a disk_log handler at startup of the Kernel application.
See an example of this below.</p>
- <p>The handler has an overload protection mechanism that will keep the handler
- process and the Kernel application alive during a high load of log
- requests. How this feature works, and how to modify the configuration,
- is described in the
+ <p>The handler has an overload protection mechanism that keeps the handler
+ process and the Kernel application alive during high loads of log
+ events. How overload protection works, and how to configure it, is
+ described in the
<seealso marker="logger_chapter#overload_protection"><c>User's Guide</c>
</seealso>.</p>
<p>To add a new instance of the disk_log handler, use
<seealso marker="logger#add_handler-3"><c>logger:add_handler/3</c>
- </seealso>. The handler configuration argument is a map which may contain
+ </seealso>. The handler configuration argument is a map which can contain
general configuration parameters, as documented in the
<seealso marker="logger_chapter#handler_configuration"><c>User's Guide</c>
- </seealso>, as well as handler specific parameters.</p>
- <p>The settings for the disk_log log file should be specified with the
- key <c>disk_log_opts</c>. These settings are a subset of the disk_log
- data type
- <seealso marker="disk_log#open-1"><c>dlog_option()</c></seealso>.</p>
- <p>Parameters in the <c>disk_log_opts</c> map:</p>
+ </seealso>, and handler specific parameters. The specific data
+ is stored in a sub map with the key <c>config</c>, and can contain the
+ following parameters:</p>
<taglist>
<tag><c>file</c></tag>
- <item>This is the full name of the disk_log log file.</item>
+ <item>
+ <p>This is the full name of the disk log file. The option
+ corresponds to the <c>name</c> property in the
+ <seealso marker="disk_log#open-1"><c>dlog_option()</c></seealso>
+ datatype.</p>
+ </item>
<tag><c>type</c></tag>
- <item>This is the disk_log type, <c>wrap</c> or <c>halt</c>. The
- default value is <c>wrap</c>.</item>
+ <item>
+ <p>This is the disk log type, <c>wrap</c> or <c>halt</c>. The option
+ corresponds to the <c>type</c> property in the
+ <seealso marker="disk_log#open-1"><c>dlog_option()</c></seealso>
+ datatype.</p>
+ <p>Defaults to <c>wrap</c>.</p>
+ </item>
<tag><c>max_no_files</c></tag>
- <item>This is the maximum number of files that disk_log will use
- for its circular logging. The default value is <c>10</c>. (The setting
- has no effect on a halt log).</item>
+ <item>
+ <p>This is the maximum number of files that disk_log uses
+ for its circular logging. The option
+ corresponds to the <c>MaxNoFiles</c> element in the <c>size</c> property in the
+ <seealso marker="disk_log#open-1"><c>dlog_option()</c></seealso>
+ datatype.</p>
+ <p>Defaults to <c>10</c>.</p>
+ <p>The setting has no effect on a halt log.</p>
+ </item>
<tag><c>max_no_bytes</c></tag>
- <item>This is the maximum number of bytes that will be written to
- a log file before disk_log proceeds with the next file in order (or
- generates an error in case of a full halt log). The default value for
- a wrap log is <c>1048576</c> bytes, and <c>infinity</c> for a halt
- log.</item>
- </taglist>
- <p>Specific configuration for the handler (represented as a sub map)
- is specified with the key <c>config</c>. It may contain the
- following parameter:</p>
- <taglist>
+ <item>
+ <p>This is the maximum number of bytes that is written to
+ a log file before disk_log proceeds with the next file in order, or
+ generates an error in case of a full halt log. The option
+ corresponds to the <c>MaxNoBytes</c> element in the <c>size</c> property in the
+ <seealso marker="disk_log#open-1"><c>dlog_option()</c></seealso>
+ datatype.</p>
+ <p>Defaults to <c>1048576</c> bytes for a wrap log, and
+ <c>infinity</c> for a halt log.</p>
+ </item>
<tag><c>filesync_repeat_interval</c></tag>
<item>
- <p>This value (in milliseconds) specifies how often the handler will
- do a disk_log sync operation in order to make sure that buffered data
- gets written to disk. The handler will repeatedly attempt this
- operation, but only perform it if something has actually been logged
- since the last sync. The default value is <c>5000</c> milliseconds.
- If <c>no_repeat</c> is set as value, the repeated sync operation is
- disabled. The user can also call the
- <seealso marker="logger_disk_log_h#sync-1"><c>sync/1</c>
- </seealso> function to perform a disk_log sync.</p></item>
+ <p>This value, in milliseconds, specifies how often the handler does
+ a disk_log sync operation to write buffered data to disk. The handler attempts
+ the operation repeatedly, but only performs a new sync if something has
+ actually been logged.</p>
+ <p>Defaults to <c>5000</c> milliseconds.</p>
+ <p>If <c>no_repeat</c> is set as value, the repeated sync operation
+ is disabled. The user can also call the
+ <seealso marker="logger_disk_log_h#filesync-1"><c>filesync/1</c>
+ </seealso> function to perform a disk_log sync.</p>
+ </item>
</taglist>
- <p>There are a number of other configuration parameters available, that are
- to be used for customizing the overload protection behaviour. The same
- parameters are used both in the standard handler and the disk_log handler,
- and are documented in the
+ <p>Other configuration parameters exist, to be used for customizing
+ the overload protection behaviour. The same parameters are used both in the
+ standard handler and the disk_log handler, and are documented in the
<seealso marker="logger_chapter#overload_protection"><c>User's Guide</c>
</seealso>.</p>
- <p>Note that when changing the configuration of the handler in runtime, by
- calling
- <seealso marker="logger#set_handler_config-2"><c>logger:set_handler_config/2
- or logger:set_handler_config/3</c></seealso>, the <c>disk_log_opts</c>
- settings may not be modified.</p>
+ <p>Notice that when changing the configuration of the handler in runtime, the
+ disk_log options (<c>file</c>, <c>type</c>, <c>max_no_files</c>,
+ <c>max_no_bytes</c>) must not be modified.</p>
<p>Example of adding a disk_log handler:</p>
<code type="none">
logger:add_handler(my_disk_log_h, logger_disk_log_h,
- #{level => error,
- filter_default => log,
- disk_log_opts =>
- #{file => "./my_disk_log",
- type => wrap,
- max_no_files => 4,
- max_no_bytes => 10000},
- config =>
- #{filesync_repeat_interval => 1000}}).
+ #{config => #{file => "./my_disk_log",
+ type => wrap,
+ max_no_files => 4,
+ max_no_bytes => 10000},
+ filesync_repeat_interval => 1000}}).
</code>
- <p>In order to use the disk_log handler instead of the default standard
+ <p>To use the disk_log handler instead of the default standard
handler when starting an Erlang node, change the Kernel default logger to
- use disk_log. Example:</p>
+ use <c>logger_disk_log_h</c>. Example:</p>
<code type="none">
erl -kernel logger '[{handler,default,logger_disk_log_h,
- #{disk_log_opts => #{file => "./system_disk_log"}}}]'
+ #{config => #{file => "./system_disk_log"}}}]'
</code>
</description>
<funcs>
<func>
- <name name="sync" arity="1" clause_i="1"/>
+ <name name="filesync" arity="1" clause_i="1"/>
<fsummary>Writes buffered data to disk.</fsummary>
<desc>
<p>Write buffered data to disk.</p>
diff --git a/lib/kernel/doc/src/logger_std_h.xml b/lib/kernel/doc/src/logger_std_h.xml
index 89e11389c5..95b4baf160 100644
--- a/lib/kernel/doc/src/logger_std_h.xml
+++ b/lib/kernel/doc/src/logger_std_h.xml
@@ -33,92 +33,84 @@
<file>logger_std_h.xml</file>
</header>
<module>logger_std_h</module>
- <modulesummary>Default handler for Logger.</modulesummary>
+ <modulesummary>Standard handler for Logger.</modulesummary>
<description>
- <p>This is the default handler for Logger.
+ <p>This is the standard handler for Logger.
Multiple instances of this handler can be added to
- Logger, and each instance will print logs to <c>standard_io</c>,
- <c>standard_error</c> or to file. The default instance that starts
- with Kernel is named <c>default</c> - which is the name to be used
- for reconfiguration.</p>
- <p>The handler has an overload protection mechanism that will keep the handler
- process and the Kernel application alive during a high load of log
- requests. How this feature works, and how to modify the configuration,
- is described in the
+ Logger, and each instance prints logs to <c>standard_io</c>,
+ <c>standard_error</c>, or to file.</p>
+ <p>The handler has an overload protection mechanism that keeps the handler
+ process and the Kernel application alive during high loads of log
+ events. How overload protection works, and how to configure it, is
+ described in the
<seealso marker="logger_chapter#overload_protection"><c>User's Guide</c>
</seealso>.</p>
<p>To add a new instance of the standard handler, use
<seealso marker="logger#add_handler-3"><c>logger:add_handler/3</c>
- </seealso>. The handler configuration argument is a map which may contain
- general configuration parameters, as documented in the
+ </seealso>. The handler configuration argument is a map which can contain
+ general configuration parameters, as documented in the
<seealso marker="logger_chapter#handler_configuration"><c>User's Guide</c>
- </seealso>, as well as handler specific parameters. The specific parameters
- are stored in a sub map with the key <c>config</c>. The following
- keys and values may be specified:</p>
+ </seealso>, and handler specific parameters. The specific data
+ is stored in a sub map with the key <c>config</c>, and can contain the
+ following parameters:</p>
<taglist>
<tag><marker id="type"/><c>type</c></tag>
<item>
- <p>This will have the value <c>standard_io</c>, <c>standard_error</c>,
- <c>{file,LogFileName}</c>, or <c>{file,LogFileName,LogFileOpts}</c>,
- where <c>standard_io</c> is the default value for type. It's recommended
- to not specify <c>LogFileOpts</c> if not absolutely necessary. The
- default options used by the handler to open a file for logging are:
- <c>raw</c>, <c>append</c> and <c>delayed_write</c>. The standard
- handler does not have support for circular logging. Use the
- <seealso marker="logger_disk_log_h"><c>logger_disk_log_h</c>
- </seealso> handler for this.</p></item>
+ <p>This has the value <c>standard_io</c>, <c>standard_error</c>,
+ <c>{file,LogFileName}</c>, or <c>{file,LogFileName,LogFileOpts}</c>.</p>
+ <p> Defaults to <c>standard_io</c>.</p>
+ <p>It is recommended not to specify <c>LogFileOpts</c> unless absolutely
+ necessary. The default options used by the handler to open a file for logging are
+ <c>raw</c>, <c>append</c>, and <c>delayed_write</c>. Notice that the standard
+ handler does not have support for circular logging. Use the disk_log handler,
+ <seealso marker="logger_disk_log_h"><c>logger_disk_log_h</c></seealso>,
+ for this.</p>
+ </item>
<tag><c>filesync_repeat_interval</c></tag>
<item>
- <p>This value (in milliseconds) specifies how often the handler will
- do a file sync operation in order to make sure that buffered data gets
- written to disk. The handler will repeatedly attempt this
- operation, but only perform it if something has actually been logged
- since the last sync. The default value is <c>5000</c> milliseconds.
- If <c>no_repeat</c> is set as value, the repeated file sync operation
- is disabled, and it will be the operating system settings that determine
- how quickly or slowly data gets written to disk. The user can also call
- the <seealso marker="logger_std_h#sync-1"><c>sync/1</c></seealso>
- function to perform a file sync.</p></item>
+ <p>This value, in milliseconds, specifies how often the handler does
+ a file sync operation to write buffered data to disk. The handler attempts
+ the operation repeatedly, but only performs a new sync if something has
+ actually been logged.</p>
+ <p>Defaults to <c>5000</c> milliseconds.</p>
+ <p>If <c>no_repeat</c> is set as value, the repeated file sync operation
+ is disabled, and it is the operating system settings that determine
+ how quickly or slowly data is written to disk. The user can also call
+ the <seealso marker="logger_std_h#filesync-1"><c>filesync/1</c></seealso>
+ function to perform a file sync.</p>
+ </item>
</taglist>
- <p>There are a number of other configuration parameters available, that are
- to be used for customizing the overload protection behaviour. The same
- parameters are used both in the standard handler and the disk_log handler,
- and are documented in the
+ <p>Other configuration parameters exist, to be used for customizing
+ the overload protection behaviour. The same parameters are used both in the
+ standard handler and the disk_log handler, and are documented in the
<seealso marker="logger_chapter#overload_protection"><c>User's Guide</c>
</seealso>.</p>
- <p>Note that when changing the configuration of the handler in runtime, by
- calling
- <seealso marker="logger#set_handler_config-2"><c>logger:set_handler_config/2</c>
- </seealso>, or
- <seealso marker="logger#set_handler_config-3"><c>logger:set_handler_config/3</c>
- </seealso>,
- the <c>type</c> parameter may not be modified.</p>
+ <p>Notice that if changing the configuration of the handler in runtime,
+ the <c>type</c> parameter must not be modified.</p>
<p>Example of adding a standard handler:</p>
<code type="none">
logger:add_handler(my_standard_h, logger_std_h,
- #{level => info,
- filter_default => log,
- config =>
- #{type => {file,"./system_info.log"},
- filesync_repeat_interval => 1000}}).
+ #{config => #{type => {file,"./system_info.log"},
+ filesync_repeat_interval => 1000}}).
</code>
- <p>In order to configure the default handler (that starts initially with
- the Kernel application) to log to file instead of <c>standard_io</c>,
- change the Kernel default logger to use a file. Example:</p>
+ <p>To set the default handler, that starts initially with
+ the Kernel application, to log to file instead of <c>standard_io</c>,
+ change the Kernel default logger configuration. Example:</p>
<code type="none">
erl -kernel logger '[{handler,default,logger_std_h,
#{config => #{type => {file,"./log.log"}}}}]'
</code>
<p>An example of how to replace the standard handler with a disk_log handler
- at start up can be found in the manual of
- <seealso marker="logger_disk_log_h"><c>logger_disk_log_h</c></seealso>.</p>
+ at startup is found in the
+ <seealso marker="logger_disk_log_h"><c>logger_disk_log_h</c></seealso>
+ manual.</p>
</description>
<funcs>
<func>
- <name name="sync" arity="1" clause_i="1"/>
+ <name name="filesync" arity="1" clause_i="1"/>
<fsummary>Writes buffered data to disk.</fsummary>
<desc>
<p>Write buffered data to disk.</p>