X-Git-Url: https://git.octo.it/?a=blobdiff_plain;f=doc%2Frrdfetch.pod;h=0052aa6513b1a82b351d5e705cc5fd185f78d090;hb=dc4997373f9cc1c170bc378ff12fa2c3a23161e9;hp=c938bb545ebf08042265251b376babcd3e38f7f0;hpb=5837606887a6d81e8b1f7588525cb1c8783fb62b;p=rrdtool.git

diff --git a/doc/rrdfetch.pod b/doc/rrdfetch.pod
index c938bb5..0052aa6 100644
--- a/doc/rrdfetch.pod
+++ b/doc/rrdfetch.pod
@@ -1,141 +1,213 @@
 =head1 NAME
 
-rrdtool fetch - fetch data from an rrd.
-
-=for html <div align="right"><a href="rrdfetch.pdf">PDF</a> version.</div>
+rrdfetch - Fetch data from an RRD.
 
 =head1 SYNOPSIS
 
-B<rrdtool> B<fetch> I<filename> I<CF> 
-S<[B<--resolution>|B<-r> I<resolution>]> 
-S<[B<--start>|B<-s> I<start>]> 
-S<[B<--end>|B<-e> I<end>]> 
+B<rrdtool> B<fetch> I<filename> I<CF>
+S<[B<--resolution>|B<-r> I<resolution>]>
+S<[B<--start>|B<-s> I<start>]>
+S<[B<--end>|B<-e> I<end>]>
+S<[B<--daemon> I<address>]>
 
 =head1 DESCRIPTION
 
-The B<fetch> function is normally used internally by the graph function,
-to get data from B<RRD>s. B<fetch> will analyze the B<RRD> and
-will try to retrieve the data in the resolution requested.
+The B<fetch> function is normally used internally by the graph
+function to get data from B<RRD>s. B<fetch> will analyze the B<RRD>
+and try to retrieve the data in the resolution requested.
 The data fetched is printed to stdout. I<*UNKNOWN*> data is often
-represented by the string "NaN" depending on your OSs printf
+represented by the string "NaN" depending on your OS's printf
 function.
 
 =over 8
 
-=item I<filename> 
+=item I<filename>
 
 the name of the B<RRD> you want to fetch the data from.
 
-=item I<CF> 
+=item I<CF>
 
-which consolidation function should have been applied to the data you
-want to fetch? (AVERAGE,MIN,MAX,LAST)
+the consolidation function that is applied to the data you
+want to fetch (AVERAGE,MIN,MAX,LAST)
 
 =item B<--resolution>|B<-r> I<resolution> (default is the highest resolution)
 
-what interval should the values have (seconds per value). B<rrdfetch> will try
-to match your request, but it will return data even if no absolute
-match is possible.
+the interval you want the values to have (seconds per
+value). B<rrdfetch> will try to match your request, but it will return
+data even if no absolute match is possible. B<NB.> See note below.
 
 =item B<--start>|B<-s> I<start> (default end-1day)
 
-when should the data begin. A time in seconds since epoch (1970-01-01)
-is required. Negative numbers are relative to the current time. By default
+start of the time series. A time in seconds since epoch (1970-01-01)
+is required. Negative numbers are relative to the current time. By default,
 one day worth of data will be fetched. See also AT-STYLE TIME SPECIFICATION
-section for a detailed explanation on  ways to specify start time.
+section for a detailed explanation on  ways to specify the start time.
 
 =item B<--end>|B<-e> I<end> (default now)
 
-when should the data end. Time in seconds since epoch. See also
-AT-STYLE TIME SPECIFICATION section for a detailed explanation of how to specify
-end time.
+the end of the time series in seconds since epoch. See also AT-STYLE
+TIME SPECIFICATION section for a detailed explanation of how to
+specify the end time.
+
+=item B<--daemon> I<address>
+
+Address of the L<rrdcached> daemon. If specified, a C<flush> command is sent
+to the server before reading the RRD files. This allows B<rrdtool> to return
+fresh data even if the daemon is configured to cache values for a long time.
+For a list of accepted formats, see the B<-l> option in the L<rrdcached> manual.
+
+ rrdtool fetch --daemon unix:/var/run/rrdcached.sock /var/lib/rrd/foo.rrd AVERAGE
+
+=back
+
+=head2 RESOLUTION INTERVAL
+
+In order to get RRDtool to fetch anything other than the finest resolution RRA
+B<both> the start and end time must be specified on boundaries that are
+multiples of the desired resolution. Consider the following example:
+
+ rrdtool create subdata.rrd -s 10 DS:ds0:GAUGE:300:0:U \
+  RRA:AVERAGE:0.5:30:3600 \
+  RRA:AVERAGE:0.5:90:1200 \
+  RRA:AVERAGE:0.5:360:1200 \
+  RRA:MAX:0.5:360:1200 \
+  RRA:AVERAGE:0.5:8640:600 \
+  RRA:MAX:0.5:8640:600
+
+This RRD collects data every 10 seconds and stores its averages over 5
+minutes, 15 minutes, 1 hour, and 1 day, as well as the maxima for 1 hour
+and 1 day.
+
+Consider now that you want to fetch the 15 minute average data for the
+last hour.  You might try
+
+ rrdtool fetch subdata.rrd AVERAGE -r 900 -s -1h
+
+However, this will almost always result in a time series that is
+B<NOT> in the 15 minute RRA. Therefore, the highest resolution RRA,
+i.e. 5 minute averages, will be chosen which in this case is not
+what you want.
+
+Hence, make sure that
+
+=over 3
+
+=item 1.
+
+both start and end time are a multiple of 900
+
+=item 2.
+
+both start and end time are within the desired RRA
 
 =back
 
+So, if time now is called "t", do
+
+ end time == int(t/900)*900,
+ start time == end time - 1hour,
+ resolution == 900.
+
+Using the bash shell, this could look be:
+
+ TIME=$(date +%s)
+ RRDRES=900
+ rrdtool fetch subdata.rrd AVERAGE -r $RRDRES \
+    -e $(($TIME/$RRDRES*$RRDRES)) -s e-1h
+
+Or in Perl:
+
+ perl -e '$ctime = time; $rrdres = 900; \
+          system "rrdtool fetch subdata.rrd AVERAGE \
+                  -r $rrdres -e @{[int($ctime/$rrdres)*$rrdres]} -s e-1h"'
+
+
 =head2 AT-STYLE TIME SPECIFICATION
 
-Apart from the traditional I<Seconds since epoch>, rrdtool does also
-understand at-style time specification.  The specification is called
-"at-style" after Unix command at(1) that has moderately complex ways
-to specify time to run your job at.  The at-style specification
-consists of two parts: B<TIME REFERENCE> specification and B<TIME
-OFFSET> specification.
+Apart from the traditional I<Seconds since epoch>, RRDtool does also
+understand at-style time specification. The specification is called
+"at-style" after the Unix command at(1) that has moderately complex
+ways to specify time to run your job at a certain date and time. The
+at-style specification consists of two parts: the B<TIME REFERENCE>
+specification and the B<TIME OFFSET> specification.
 
 =head2 TIME REFERENCE SPECIFICATION
 
-Time reference specification is used, well,... to establish a reference
-moment in time (for time offset to be applied to). When present,
+The time reference specification is used, well, to establish a reference
+moment in time (to which the time offset is then applied to). When present,
 it should come first, when omitted, it defaults to B<now>. On its own part,
-time reference consists of I<time-of-day> reference (which should come
-first, if present) and I<day> reference.
+time reference consists of a I<time-of-day> reference (which should come
+first, if present) and a I<day> reference.
 
-I<Time-of-day> can be specified as B<HH:MM>, B<HH.MM>,
-or just B<HH>, you can suffix it with B<am> or B<pm> or use
-24-hours clock. The few special times of day are understood as well,
-these include B<midnight> (00:00), B<noon> (12:00) and British
+The I<time-of-day> can be specified as B<HH:MM>, B<HH.MM>,
+or just B<HH>. You can suffix it with B<am> or B<pm> or use
+24-hours clock. Some special times of day are understood as well,
+including B<midnight> (00:00), B<noon> (12:00) and British
 B<teatime> (16:00).
 
-The I<day> can be specified as I<month-name> I<day-of-the-month>
-and optional 2- or 4-digit I<year> number (e.g. March 8 1999).
-Alternatively, you can use I<day-of-week-name> (e.g. Monday),
-or one of the words: B<yesterday>, B<today>, B<tomorrow>.
-You can also specify I<day> as a full date in several numerical formats;
-these include: B<MM/DD/[YY]YY>, B<DD.MM.[YY]YY>, B<YYYYMMDD>.
+The I<day> can be specified as I<month-name> I<day-of-the-month> and
+optional a 2- or 4-digit I<year> number (e.g. March 8 1999). Alternatively,
+you can use I<day-of-week-name> (e.g. Monday), or one of the words:
+B<yesterday>, B<today>, B<tomorrow>. You can also specify the I<day> as a
+full date in several numerical formats, including B<MM/DD/[YY]YY>,
+B<DD.MM.[YY]YY>, or B<YYYYMMDD>.
 
-I<NOTE1>: this is different from the original at(1) behavior,
-which interprets a single-number date as MMDD[YY]YY.
+I<NOTE1>: this is different from the original at(1) behavior, where a
+single-number date is interpreted as MMDD[YY]YY.
 
-I<NOTE2>: if you specify I<day> this way, the I<time-of-day> is REQUIRED
-to be present.
+I<NOTE2>: if you specify the I<day> in this way, the I<time-of-day> is
+REQUIRED as well.
 
-Finally, you can use words B<now>, B<start>, or B<end> as your time
-reference. B<Now> refers to the current moment (and is also a default
-time reference). B<Start> (B<end>) can be used to specify time
+Finally, you can use the words B<now>, B<start>, or B<end> as your time
+reference. B<Now> refers to the current moment (and is also the default
+time reference). B<Start> (B<end>) can be used to specify a time
 relative to the start (end) time for those tools that use these
-categories (rrdfetch, rrdgraph).
+categories (B<rrdfetch>, L<rrdgraph>).
 
-Month and weekday names can be used in their naturally abbreviated form
-(e.g., Dec for December, Sun for Sunday, etc.). The words B<now>,
-B<start>, B<end> can be abbreviated to B<n>, B<s>, B<e>.
+Month and day of the week names can be used in their naturally
+abbreviated form (e.g., Dec for December, Sun for Sunday, etc.). The
+words B<now>, B<start>, B<end> can be abbreviated as B<n>, B<s>, B<e>.
 
 =head2 TIME OFFSET SPECIFICATION
 
-Time offset specification is used to add (or subtract) certain time
-interval to (from) the time reference moment. It consists of I<sign>
-(S<B<+> or B<->>) and I<amount>. The following time units can be used
-to specify the I<amount>: B<years>, B<months>, B<weeks>, B<days>,
-B<hours>, B<minutes>, B<seconds>, these can be used in singular
-or plural form, and abbreviated naturally or to a single letter
-(e.g. +3days, -1wk, -3y). Several time units can be combined
-together (e.g., -5mon1w2d), as well as several time offsets can be
-concatenated (e.g., -5h45min = -5h-45min = -6h+15min = -7h+1h30m-15min, etc.)
+The time offset specification is used to add/subtract certain time
+intervals to/from the time reference moment. It consists of a I<sign>
+(S<B<+> or B<->>) and an I<amount>. The following time units can be
+used to specify the I<amount>: B<years>, B<months>, B<weeks>, B<days>,
+B<hours>, B<minutes>, or B<seconds>. These units can be used in
+singular or plural form, and abbreviated naturally or to a single
+letter (e.g. +3days, -1wk, -3y). Several time units can be combined
+(e.g., -5mon1w2d) or concatenated (e.g., -5h45min = -5h-45min =
+-6h+15min = -7h+1h30m-15min, etc.)
 
 I<NOTE3>: If you specify time offset in days, weeks, months, or years,
-you will end with the time offset that may vary depending on you time
+you will end with the time offset that may vary depending on your time
 reference, because all those time units have no single well defined
 time interval value (S<1 year> contains either 365 or 366 days, S<1 month>
 is 28 to 31 days long, and even S<1 day> may be not equal to 24 hours
 twice a year, when DST-related clock adjustments take place).
 To cope with this, when you use days, weeks, months, or years
 as your time offset units your time reference date is adjusted
-accordingly without taking too much further effort to ensure anything
+accordingly without too much further effort to ensure anything
 about it (in the hope that mktime(3) will take care of this later).
 This may lead to some surprising (or even invalid!) results,
 e.g. S<'May 31 -1month'> = S<'Apr 31'> (meaningless) = S<'May 1'>
 (after mktime(3) normalization); in the EET timezone
 '3:30am Mar 29 1999 -1 day' yields '3:30am Mar 28 1999' (Sunday)
-which is invalid time/date combination (because of 3am -> 4am DST
+which is an invalid time/date combination (because of 3am -> 4am DST
 forward clock adjustment, see the below example).
-On the other hand, hours, minutes, and seconds are well defined time
+
+In contrast, hours, minutes, and seconds are well defined time
 intervals, and these are guaranteed to always produce time offsets
-exactly as specified (e.g. for EET timezone, S<'8:00 Mar 27 1999 +2 days'> =
-S<'8:00 Mar 29 1999'>, but since there is 1-hour DST forward clock adjustment
-takes place around S<3:00 Mar 28 1999>, the actual time interval between
-S<8:00 Mar 27 1999> and S<8:00 Mar 29 1999> equals 47 hours; on the other hand,
-S<'8:00 Mar 27 1999 +48 hours'> = S<'9:00 Mar 29 1999'>, as expected)
+exactly as specified (e.g. for EET timezone, S<'8:00 Mar 27 1999 +2
+days'> = S<'8:00 Mar 29 1999'>, but since there is 1-hour DST forward
+clock adjustment that occurs around S<3:00 Mar 28 1999>, the actual
+time interval between S<8:00 Mar 27 1999> and S<8:00 Mar 29 1999>
+equals 47 hours; on the other hand, S<'8:00 Mar 27 1999 +48 hours'> =
+S<'9:00 Mar 29 1999'>, as expected)
 
 I<NOTE4>: The single-letter abbreviation for both B<months> and B<minutes>
-is B<m>. To disambiguate, the parser tries to read your S<mind :)>
+is B<m>. To disambiguate them, the parser tries to read your S<mind :)>
 by applying the following two heuristics:
 
 =over 3
@@ -145,26 +217,26 @@ by applying the following two heuristics:
 If B<m> is used in context of (i.e. right after the) years,
 months, weeks, or days it is assumed to mean B<months>, while
 in the context of hours, minutes, and seconds it means minutes.
-(e.g., in -1y6m or +3w1m B<m> means B<months>, while in
--3h20m or +5s2m B<m> means B<minutes>)
+(e.g., in -1y6m or +3w1m B<m> is interpreted as B<months>, while in
+-3h20m or +5s2m B<m> the parser decides for B<minutes>).
 
 =item 2
 
 Out of context (i.e. right after the B<+> or B<-> sign) the
 meaning of B<m> is guessed from the number it directly follows.
-Currently, if the number absolute value is below 25 it is assumed
+Currently, if the number's absolute value is below 25 it is assumed
 that B<m> means B<months>, otherwise it is treated as B<minutes>.
 (e.g., -25m == -25 minutes, while +24m == +24 months)
 
 =back
 
 I<Final NOTES>: Time specification is case-insensitive.
-Whitespace can be inserted freely or omitted altogether,
-there are, however, cases when whitespace is required
+Whitespace can be inserted freely or omitted altogether.
+There are, however, cases when whitespace is required
 (e.g., S<'midnight Thu'>). In this case you should either quote the
 whole phrase to prevent it from being taken apart by your shell or use
 '_' (underscore) or ',' (comma) which also count as whitespace
-(e.g., midnight_Thu or midnight,Thu)
+(e.g., midnight_Thu or midnight,Thu).
 
 
 =head2 TIME SPECIFICATION EXAMPLES
@@ -172,30 +244,45 @@ whole phrase to prevent it from being taken apart by your shell or use
 I<Oct 12> -- October 12 this year
 
 I<-1month> or I<-1m> -- current time of day, only a month before
-(may yield surprises, see the NOTE3 above)
+(may yield surprises, see NOTE3 above).
 
-I<noon yesterday -3hours> -- yesterday morning; can be put also as I<9am-1day>
+I<noon yesterday -3hours> -- yesterday morning; can also be specified
+as I<9am-1day>.
 
-I<23:59 31.12.1999> -- 1 minute to the year 2000
+I<23:59 31.12.1999> -- 1 minute to the year 2000.
 
-I<12/31/99 11:59pm> -- 1 minute to the year 2000 for imperialists
+I<12/31/99 11:59pm> -- 1 minute to the year 2000 for imperialists.
 
 I<12am 01/01/01> -- start of the new millennium
 
 I<end-3weeks> or I<e-3w> -- 3 weeks before end time
-(may be used as start time specification)
+(may be used as start time specification).
 
 I<start+6hours> or I<s+6h> -- 6 hours after start time
-(may be used as end time specification)
+(may be used as end time specification).
 
 I<931225537> -- 18:45  July 5th, 1999
-(yes, seconds since 1970 are valid as well)
+(yes, seconds since 1970 are valid as well).
 
 I<19970703 12:45> -- 12:45  July 3th, 1997
-(not quote standard, but I love this ...)
+(my favorite, and its even got an ISO number (8601)).
+
+=head1 ENVIRONMENT VARIABLES
+
+The following environment variables may be used to change the behavior of
+C<rrdtoolE<nbsp>fetch>:
 
+=over 4
+
+=item B<RRDCACHED_ADDRESS>
+
+If this environment variable is set it will have the same effect as specifying
+the C<--daemon> option on the command line. If both are present, the command
+line argument takes precedence.
+
+=back
 
 =head1 AUTHOR
 
-Tobias Oetiker <oetiker@ee.ethz.ch>
+Tobias Oetiker E<lt>tobi@oetiker.chE<gt>