- matcher=<matcher-name>
Defines the nature of the matching that will be
performed. Depending on the name supplied, this may be positional matching
using celestial or Cartesian coordinates, exact matching on the value of a
string column, or other things. A list and explanation of the available
matching algorithms is given in SUN/256. The value supplied for this parameter
determines the meanings of the values required by the
params,
values* and
tuning parameter(s).
- params=<match-params>
Determines the parameters of this match. This is
typically one or more tolerances such as error radii. It may contain zero or
more values; the values that are required depend on the match type selected by
the
matcher parameter. If it contains multiple values, they must be
separated by spaces; values which contain a space can be 'quoted' or
"quoted".
- tuning=<tuning-params>
Tuning values for the matching process, if appropriate.
It may contain zero or more values; the values that are permitted depend on
the match type selected by the
matcher parameter. If it contains
multiple values, they must be separated by spaces; values which contain a
space can be 'quoted' or "quoted". If this optional parameter is not
supplied, sensible defaults will be chosen.
- values=<expr-list>
Defines the values from the input table which are used to
determine whether a match has occurred. These will typically be coordinate
values such as RA and Dec and perhaps some per-row error values as well,
though exactly what values are required is determined by the kind of match as
determined by
matcher. Depending on the kind of match, the number and
type of the values required will be different. Multiple values should be
separated by whitespace; if whitespace occurs within a single value it must be
'quoted' or "quoted". Elements of the expression list are commonly
just column names, but may be algebraic expressions calculated from zero or
more columns as explained in SUN/256.
- action=identify|keep0|keep1|wide2|wideN
Determines the form of the table which will be output as
a result of the internal match.
- identify: The output table is the same as the input table except
that it contains two additional columns, GroupID and
GroupSize, following the input columns. Each group of rows which
matched is assigned a unique integer, recorded in the GroupID column, and
the size of each group is recorded in the GroupSize column. Rows which
don't match any others (singles) have null values in both these
columns.
- keep0: The result is a new table containing only "single"
rows, that is ones which don't match any other rows in the table. Any
other rows are thrown out.
- keep1: The result is a new table in which only one row (the first
in the input table order) from each group of matching ones is retained. A
subsequent intra-table match with the same criteria would therefore show
no matches.
- wideN: The result is a new "wide" table consisting of
matched rows in the input table stacked next to each other. Only groups of
exactly N rows in the input table are used to form the output table; each
row of the output table consists of the columns of the first group member,
followed by the columns of the second group member and so on. The output
table therefore has N times as many columns as the input table. The column
names in the new table have _1, _2, ... appended to them to
avoid duplication.
- progress=none|log|time|profile
Determines whether information on progress of the match
should be output to the standard error stream as it progresses. For lengthy
matches this is a useful reassurance and can give guidance about how much
longer it will take. It can also be useful as a performance diagnostic.
The options are:
- none: no progress is shown
- log: progress information is shown
- time: progress information and some time profiling information is
shown
- profile: progress information and limited time/memory profiling
information are shown
- runner=parallel|parallel<n>|parallel-all|sequential|classic|partest
Selects the threading implementation. The options are
currently:
- parallel: uses multithreaded implementation for large tables, with
default parallelism, which is the smaller of 6 and the number of available
processors
- parallel<n>: uses multithreaded implementation for large
tables, with parallelism given by the supplied value <n>
- parallel-all: uses multithreaded implementation for large tables,
with a parallelism given by the number of available processors
- sequential: uses multithreaded implementation but with only a
single thread
- classic: uses legacy sequential implementation
- partest: uses multithreaded implementation even when tables are
small
The
parallel* options should normally run faster than
sequential
or
classic (which are provided mainly for testing purposes), at least
for large matches and where multiple processing cores are available.
The default value "parallel" is currently limited
to a parallelism of 6 since larger values yield diminishing returns given
that some parts of the matching algorithms run sequentially (Amdahl's Law),
and using too many threads can sometimes end up doing more work or impacting
on other operations on the same machine. But you can experiment with other
concurrencies, e.g. "parallel16" to run on 16 cores (if
available) or "parallel-all" to run on all available
cores.
The value of this parameter should make no difference to the
matching results. If you notice any discrepancies please report
them.
- ifmt=<in-format>
Specifies the format of the input table as specified by
parameter
in. The known formats are listed in SUN/256. This flag can be
used if you know what format your table is in. If it has the special value
(auto) (the default), then an attempt will be made to detect the format
of the table automatically. This cannot always be done correctly however, in
which case the program will exit with an error explaining which formats were
attempted. This parameter is ignored for scheme-specified tables.
- istream=true|false
If set true, the input table specified by the
in
parameter will be read as a stream. It is necessary to give the
ifmt
parameter in this case. Depending on the required operations and processing
mode, this may cause the read to fail (sometimes it is necessary to read the
table more than once). It is not normally necessary to set this flag; in most
cases the data will be streamed automatically if that is the best thing to do.
However it can sometimes result in less resource usage when processing large
files in certain formats (such as VOTable). This parameter is ignored for
scheme-specified tables.
- in=<table>
The location of the input table. This may take one of the
following forms:
- A filename.
- A URL.
- The special value "-", meaning standard input. In this
case the input format must be given explicitly using the ifmt
parameter. Note that not all formats can be streamed in this way.
- A scheme specification of the form
:<scheme-name>:<scheme-args>.
- A system command line with either a "<" character at
the start, or a "|" character at the end
("<syscmd" or "syscmd|"). This
executes the given pipeline and reads from its standard output. This will
probably only work on unix-like systems.
In any case, compressed data in one of the supported compression formats (gzip,
Unix compress or bzip2) will be decompressed transparently.
- icmd=<cmds>
Specifies processing to be performed on the input table
as specified by parameter
in, before any other processing has taken
place. The value of this parameter is one or more of the filter commands
described in SUN/256. If more than one is given, they must be separated by
semicolon characters (";"). This parameter can be repeated multiple
times on the same command line to build up a list of processing steps. The
sequence of commands given in this way defines the processing pipeline which
is performed on the table.
Commands may alteratively be supplied in an external file, by
using the indirection character '@'. Thus a value of
"@filename" causes the file filename to be read for
a list of filter commands to execute. The commands in the file may be
separated by newline characters and/or semicolons, and lines which are blank
or which start with a '#' character are ignored.
- ocmd=<cmds>
Specifies processing to be performed on the output table,
after all other processing has taken place. The value of this parameter is one
or more of the filter commands described in SUN/256. If more than one is
given, they must be separated by semicolon characters (";"). This
parameter can be repeated multiple times on the same command line to build up
a list of processing steps. The sequence of commands given in this way defines
the processing pipeline which is performed on the table.
Commands may alteratively be supplied in an external file, by
using the indirection character '@'. Thus a value of
"@filename" causes the file filename to be read for
a list of filter commands to execute. The commands in the file may be
separated by newline characters and/or semicolons, and lines which are blank
or which start with a '#' character are ignored.
- omode=out|meta|stats|count|checksum|cgi|discard|topcat|samp|tosql|gui
The mode in which the result table will be output. The
default mode is
out, which means that the result will be written as a
new table to disk or elsewhere, as determined by the
out and
ofmt parameters. However, there are other possibilities, which
correspond to uses to which a table can be put other than outputting it, such
as displaying metadata, calculating statistics, or populating a table in an
SQL database. For some values of this parameter, additional parameters
(
<mode-args>) are required to determine the exact behaviour.
Possible values are
- out
- meta
- stats
- count
- checksum
- cgi
- discard
- topcat
- samp
- tosql
- gui
Use the
help=omode flag or see SUN/256 for more information.
- out=<out-table>
The location of the output table. This is usually a
filename to write to. If it is equal to the special value "-" (the
default) the output table will be written to standard output.
This parameter must only be given if omode has its default
value of "out".
- ofmt=<out-format>
Specifies the format in which the output table will be
written (one of the ones in SUN/256 - matching is case-insensitive and you can
use just the first few letters). If it has the special value
"
(auto)" (the default), then the output filename will be
examined to try to guess what sort of file is required usually by looking at
the extension. If it's not obvious from the filename what output format is
intended, an error will result.
This parameter must only be given if omode has its default
value of "out".