PQCREATE

pqcreate - program to create a Unidata LDM product queue

pqcreate [-v] [-c] [-s size] [-S nproducts] [-q pqfname]

This program creates a LDM product queue (see pq(3)). A product queue is currently implemented as a memory-mapped file, and hence should be created on a disk local to the host on which programs sharing the product queue will be run. The current release of the queue software does not allow the queue to grow, so this program must be used to create a (fixed size) queue of adequate size prior to running any of the LDM programs.

The current queue implementation file format has 3 parts, a fixed size header, a data section, and a control or index section. The size of the data section is specified by the -s option. The index section is parameterized by the number of product "slots" available. This is set by the -S option.

-v

Verbose output. A line is output on queue creation that confirms the queue of the specified size was successfully created. The default is not to output such a message.

-c

Used to clobber an existing product queue with the same pathname, if it already exists, before creating a new product queue. If this option is not specified, the program will exit with an error message when requested to create a product queue that already exists. If processes that insert data into a product queue are terminated ungracefully (for example as the result of a system crash), the leftover queue may be corrupt and hence should be clobbered when the LDM is restarted.

−s size

Specifies the requested size, in bytes, of the data portion of the product queue. This "option" is required. If the last character of size is a (case insensitive) ‘K’, ‘M’, or G’, then the preceeding numeric value specifies kilobytes, megabytes, or gigabytes, respectively. A larger product queue can hold more or larger data products and hence deal with longer network outages to downstream data sinks or with slow decoders. The actual size of the data portion of the product queue might be slightly greater than the requested size for performance reasons.

−S nproducts

This option specifies the number of product slots available in the index section of the queue file. If unspecified, the number of slots will be the option-argument of the -s option divided by an assumed average product size -- which is guaranteed to be incorrect.

−q pqfname

The name of the product queue file. The default is /data/var/queues/ldm.pq. This should specify a local file, not a remotely mounted file.

-f

Fast option, to create a product queue quickly without allocating all the disk blocks it requires. This creates a sparse file with mostly zero blocks that occupy no space on disk until they are written. This is not the default because it permits creating a product queue larger than the available disk space, or larger than the space that will be available at some later time. This option should only be used if you know there will be enough disk space for the product queue when it is full.

The following invocation will create a product queue of 50 Mbytes in /usr/local/ldm/data/ldm.pq:

pqcreate -s 50M -q /usr/local/ldm/data/ldm.pq

ldmd(1), ldmadmin(1), pq(3), WWW URL http://www.unidata.ucar.edu/software/ldm/.