# &adminguide;

## Overview

The sql_cacher module introduces the possibility to cache data from a SQL-based database (using different &osips; modules which implement the DB API) into a cache system implemented in &osips; through the CacheDB Interface. This is done by specifying the databases URLs, SQL table to be used, desired columns to be cached and other details in the &osips; configuration script.

The cached data is available in the script through the read-only pseudovariable $sql_cached_value similar to a Key-Value system. A specified column from the SQL table has the role of key therefore the value of this column along with the name of a required column are provided as "parameters" to the pseudovariable returning the appropriate value of the column.

There are two types of caching available:

- full caching - the entire SQL table (all the rows) is loaded into the cache at &osips; startup;

- on demand - the rows of the SQL table are loaded at runtime when appropriate keys are requested.

For on demand caching, the stored values have a configurable expire period after which they are permanently removed unless an MI reload function is called for a specific key. In the case of full caching the data is automatically reloaded at a configurable interval. Consequently if the data in the SQL database changes and a MI reload function is called, the old data remains in cache only until it expires.

## Dependencies

The following modules must be loaded before this module:

- The &osips; modules that offer actual database back-end connection

## Exported Parameters

### `cache_table` (string)

This parameter can be set multiple times in order to cache multiple SQL tables or even the same table but with a different configuration. The module distinguishes those different entries by an id string.

The caching entry is specified via this parameter that has it's own subparameters. Each of those parameters are separted by a configurable delimiter and have the following format:

param_name=param_value

The parameters are:

- id : cache entry id

- db_url : the URL of the SQL database

- cachedb_url : the URL of the CacheDB database

- table : SQL database table name

- key : SQL database column name of the key column

- columns : names of the columns to be cached from the SQL database, separated by a configurable delimiter

  If not present, all the columns from the table will be cached

- on_demand : specifies the type of caching:

  - 0 : full caching

  - 1 : on demand

  If not present, default value is 0

- expire : expire period for the values stored in the cache for the on demand caching type in seconds

  If not present, default value is 1 hour

The parameters must be given in the exact order specified above.

Overall, the parameter does not have a default value, it must be set at least once in order to cache any table.

#### `cache_table` parameter usage

    modparam("sql_cacher", "cache_table",
    "id=caching_name
    db_url=mysql://root:opensips@localhost/opensips_2_2
    cachedb_url=mongodb:mycluster://127.0.0.1:27017/db.col
    table=table_name
    key=column_name_0
    columns=column_name_1 column_name_2 column_name_3
    on_demand=0")

### `spec_delimiter` (string)

The delimiter to be used in the caching entry specification provided in the cache_table parameter to separate the subparameters. It must be a single character.

The default value is newline.

#### `spec_delimiter` parameter usage

    modparam("sql_cacher", "spec_delimiter", "\n")

### `pvar_delimiter` (string)

The delimiter to be used in the $sql_cached_value pseudovariable to separate the caching id, the desired column name and the value of the key. It must be a single character.

The default value is :.

#### `pvar_delimiter` parameter usage

    modparam("sql_cacher", "pvar_delimiter", " ")

### `columns_delimiter` (string)

The delimiter to be used in the columns subparameter of the caching entry specification provided in the cache_table parameter to separate the desired columns names. It must be a single character.

The default value is (space).

#### `columns_delimiter` parameter usage

    modparam("sql_cacher", "columns_delimiter", ",")

### `sql_fetch_nr_rows` (integer)

The number of rows to be fetched into &osips; private memory in one chunk from the SQL database driver. When querying large tables, adjust this parameter accordingly to avoid the filling of &osips; private memory.

The default value is 100.

#### `sql_fetch_nr_rows` parameter usage

    modparam("sql_cacher", "sql_fetch_nr_rows", "1000")

### `full_caching_expire` (integer)

Expire period for the values stored in cache for the full caching type in seconds. This is the longest time that deleted or modified data remains in cache.

The default value is 24 hours.

#### `full_caching_expire` parameter usage

    modparam("sql_cacher", "full_caching_expire", "3600")

### `reload_interval` (integer)

This parameter represents how many seconds before the data expires (for full caching) the automatic reloading is triggerd.

The default value is 60 s.

#### `reload_interval` parameter usage

    modparam("sql_cacher", "reload_interval", "5")

## Exported Functions

No function exported to be used from configuration file.

## MI Commands

### `sql_cacher_reload`

Reloads the entire SQL table in cache for full caching or the specified key for on demand caching.

The first parameter is the caching id.

The second parameter must be a value of the key column from the SQL table. For full caching this parameter is not needed.

#### `sql_cacher_reload` usage

    ...
    $ opensipsctl fifo sql_cacher_reload caching_name
    ...
    $ opensipsctl fifo sql_cacher_reload caching_name key
    ...

## Exported pseudo-variables

### `$sql_cached_value(id{sep}col{sep}key)`

The cached data is available through this read-only PV.The format is the following:

- sep : separator configured by pvar_delimiter parameter

- id : cache entry id

- col : name of the required column

- key : value of the key column

#### `sql_cached_value(id{sep}col{sep}key) pseudo-variable` usage

    ...
    $avp(a) = $sql_cached_value(caching_name:column_name_1:key1);
    ...

## Usage Example

This section provides an usage example for the caching of an SQL table.

Suppose one in interested in caching the columns: host_name, reply_code, flags and next_domain from the carrierfailureroute table of the &osips; database.

### Example database content - carrierfailureroute table

    ...
    +----+---------+-----------+------------+--------+-----+-------------+
    | id | domain  | host_name | reply_code | flags | mask | next_domain |
    +----+---------+-----------+------------+-------+------+-------------+
    |  1 |      99 |           | 408        |    16 |   16 |             |
    |  2 |      99 | gw1       | 404        |     0 |    0 | 100         |
    |  3 |      99 | gw2       | 50.        |     0 |    0 | 100         |
    |  4 |      99 |           | 404        |  2048 | 2112 | asterisk-1  |
    +----+---------+-----------+------------+-------+------+-------------+
    ...

In the first place, the details of the caching must be provided by setting the module parameter cache_table in the &osips; configuration script.

### Setting the `cache_table` parameter

    modparam("sql_cacher", "cache_table",
    "id=carrier_fr_caching
    db_url=mysql://root:opensips@localhost/opensips
    cachedb_url=mongodb:mycluster://127.0.0.1:27017/my_db.col
    table=carrierfailureroute
    key=id
    columns=host_name reply_code flags next_domain")

Next, the values of the cached columns ca be accessed through the $sql_cached_value PV.

### Accessing cached values

    ...
    $avp(rc1) = $sql_cached_value(carrier_fr_caching:reply_code:1);
    $avp(rc2) = $sql_cached_value(carrier_fr_caching:reply_code:2);
    ...
    var(some_id)=4;
    $avp(nd) = $sql_cached_value(carrier_fr_caching:next_domain:$var(some_id));
    ...
    xlog("host name is: $sql_cached_value(carrier_fr_caching:host_name:2)");
    ...