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RRDtool refers to round robin database tool. Round robin databases have a fixed number of data points in them and contain a pointer to the current element. Since the databases have a fixed number of data points the database size doesn't change after creation. RRDtool allows you to define a set of archives which consolidate the primary data points in higher granularity. RRDtool is specialized for time series data and can be used to create RRD files, update RRDs, retreive data from RRDs, and generate graphs from the databases. This module provides a POE wrapper around the rrdtool command line interface.

HyperSQL HSQLDB is the leading SQL relational database engine written in Java. It has a JDBC driver and supports a rich subset of ANSI-92 SQL (BNF tree format) plus SQL 99 and 2003 enhancements. It offers a small (less than 100k in one version for applets), fast database engine which offers both in-memory and disk-based tables and supports embedded and server modes. Additionally, it includes tools such as a minimal web server, in-memory query and management tools (can be run as applets) and a number of demonstration examples.

CFFI, the Common Foreign Function Interface, purports to be a portable foreign function interface for Common Lisp. The CFFI library is composed of a Lisp-implementation-specific backend in the CFFI-SYS package, and a portable frontend in the CFFI package. The CFFI-SYS backend package defines a low-level interface to the native FFI support in the Lisp implementation. It offers operators for allocating and dereferencing foreign memory, calling foreign functions, and loading shared libraries. The CFFI frontend provides a declarative interface for defining foreign functions, structures, typedefs, enumerated types, etc. It is implemented in portable ANSI CL making use of the low-level operators exported by CFFI-SYS.

Log::Dispatch is a suite of OO modules for logging messages to multiple outputs, each of which can have a minimum and maximum log level. It is designed to be easily subclassed, both for creating a new dispatcher object and particularly for creating new outputs. It also allows both global (dispatcher level) and local (logging object) message formatting callbacks which allows greater flexibility and should reduce the need for subclassing. Subclassing is only needed to send a message to a different output, not to change the message format.

This driver uses a database table to store the cache for CHI. The newest versions of MySQL and SQLite are known to work. Other RDBMSes should work. Why cache things in a database? Isn't the database what people are trying to avoid with caches? This is often true, but a simple primary key lookup is extremely fast in many databases and this provides a shared cache that can be used when less reliable storage like memcached is not appropriate. Also, the speed of simple lookups on MySQL when accessed over a local socket is very hard to beat. DBI is fast.

The Carp routines are useful in your own modules because they act like die() or warn(), but with a message which is more likely to be useful to a user of your module. In the case of cluck, confess, and longmess that context is a summary of every call in the call-stack. For a shorter message you can use carp or croak which report the error as being from where your module was called. There is no guarantee that that is where the error was, but it is a good educated guess.

Minilla is a CPAN module authoring tool. Minilla provides 'minil' command for authorizing a CPAN distribution. The repository created and managed by Minilla is git install ready, and cpan of course. Minilla is built on only few small libraries. You can install Minilla without a huge list of dependencies to heavy modules. Conventions: module written in Pure Perl are located in lib/; executable file is in script/ directory, if any; module is maintained with Git and git ls-files matches with what you will release; module has a static list of prerequisites that can be described in cpanfile; has a Changes file.

Consistent hashing is a scheme that provides hash table functionality in a way that the addition or removal of one slot does not significantly change the mapping of keys to slots. In contrast, in most traditional hash tables, a change in the number of array slots causes nearly all keys to be remapped. Consistent hashing was introduced in 1997 as a way of distributing requests among a changing population of web servers. More recently, it and similar techniques have been employed in distributed hash tables.

librelp is an easy to use library for the RELP protocol. RELP in turn provides reliable event logging over the network (and consequently RELP stands for Reliable Event Logging Protocol). RELP (and hence) librelp assures that no message is lost, not even when connections break and a peer becomes unavailable. The current version of RELP has a minimal window of opportunity for message duplication after a session has been broken due to network problems. In this case, a few messages may be duplicated (a problem that also exists with plain TCP syslog). Future versions of RELP will address this shortcoming.

A patch to Perl 5.005_55 by the author implements a core API for weak references. This module is a Perl-level interface to that API, allowing weak references to be created in Perl. A weak reference is just like an ordinary Perl reference except that it isn't included in the reference count of the thing referred to. This means that once all references to a particular piece of data are weak, the piece of data is freed and all the weak references are set to undef. This is particularly useful for implementing circular data structures without memory leaks or caches of objects.