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.TH mgmerge 1 \*(Dt CITRI
.SH NAME
mgmerge \- update an mg system database with new documents
.SH SYNOPSIS
.B mgmerge
[
.B \-c
]
[
.BI \-g " get"
]
[
.BI \-s " source"
]
[
.B \-S
]
[
.B \-w
]
.I collection-name
.SH DESCRIPTION
.B mgmerge
is a
.B csh
script that executes all the appropriate programs in the correct order
to completely merge a current
.BR mg (1)
system database ready with some new documents, saving the need for a complete
database rebuild with
.B mgbuild.
It does this by building a second
.BR mg (1)
system database from the new documents and then merging this database
with the old one.
This program makes use of the
.BR mg_get_merge (1)
script to obtain the text of the collection.
.B mgmerge
cannot edit or delete documents already in a database; only new documents
can be added.
.SH OPTIONS
Options can occur in any order, but the collection name must be last.
.TP "\w'\fIcollection-name\fP'u+2n"
.BI \-c
This specifies whether the
.I get
program is \*(lqcomplex\*(rq.  If a
.I get
program is \*(lqcomplex\*(rq, then it requires initialisation and
cleanup with the
.B \-i
and
.B \-c
options.
.TP
.BI \-g " get"
This specifies the program to use for getting the source text for the
build.  If no
.B \-g
option is given, the default program
.BR mg_get_merge (1)
is used.
.TP
.BI \-s " source"
The
.B mgmerge
program consists of two parts.  The first part initializes variables
to default values.  The second part uses these variables to control
how the
.BR mg (1)
database is built.  This option specifies a program to execute between
the first and second parts.  The details of what the variables are, and
how they may be changed, are in comments in the
.B mgmerge
program.
If this option is used, the program should ideally be the same one that
was called by
.BR mgbuild (1)
to build the database since some parameters need to be consistent between
.B mgbuild
and
.B mgmerge.
.TP
.B \-S
This option will cause a slow merge to be performed on the inverted files,
where each inverted file entry is decoded and recoded.
The default is a fast merge. Accumulated fast merges slowly degrade
compression performance on the resulting inverted file so
a periodic slow merge is recommended.
.TP
.B \-w
Adding new documents can have an effect on the weight of the previous ones.
By default the weights for documents already in the collection are not 
recomputed since the change in their values is usually small.
This option forces new weights to be recomputed.
Periodic use of this option, as for the "-S" option, is recomended,
otherwise query rankings may become inaccurate.
.TP
.I collection-name
This is the collection name, as required by the
.BR mg_get_merge (1)
program.  It serves both as a
.I case
statement selector, and as the name of a subdirectory that holds the
indexing files.
.SH ENVIRONMENT
.TP "\w'\fBMGDATA\fP'u+2n"
.SB MGDATA
If this environment variable exists, then its value is used as the
default directory where the
.BR mg (1)
collection files are.  If this variable does not exist, then the
directory \*(lq\fB.\fP\*(rq is used by default.  The command line
option
.BI \-d " directory"
overrides the directory in
.BR MGDATA .
Note that a temporary directory under the
.B MGDATA
directory is used to perform the merge.
The default name for this directory is
.BR MERGE .
.SH FILES
.TP 20
.B *.invf
Inverted file.
.TP
.B *.invf.dict
Compressed stemmed dictionary.
.TP
.B *.invf.dict.blocked
The `on-disk' stemmed dictionary.
.TP
.B *.invf.idx
The index into the inverted file.
.TP
.B *.weight
The exact weights file.
.TP
.B *.text
Compressed documents.
.TP
.B *.text.stats
Text statistics.
.TP
.B *.text.dict
Compressed compression dictionary.
.TP
.B *.text.idx
Index into the compressed documents.
.TP
.B *.text.idx.wgt
Interleaved index into the compressed documents and document weights.
.TP
.B *.weight.approx
Approximate document weights.
.SH "SEE ALSO"
.na
.BR mg (1),
.BR mgbuild (1),
.BR mg_get_merge (1),
.BR mg_get (1),
.BR mg_invf_merge (1),
.BR mg_text_merge (1),
.BR mg_query (1),
.BR mg_weights_build (1).