Metrics

class postgres_metrics.metrics.MetricRegistry

Bases: object

register(metric)

Given a class (not class instance) of Metric, adds it to the available list of metrics to show it to a user.

sorted

All registered metrics ordered by their label.

unregister(slug)

Remove the metric slug from the registry. Raises a KeyError if the metric isn’t registered.

class postgres_metrics.metrics.Metric(ordering=None)

Bases: object

The superclass for all Metric implementations. Inherit from this to define your own metric.

If you want to implement your own metric, here’s a gist:

from django.utils.translation import ugettext_lazy as _
from postgres_metrics.metrics import Metric, registry


class DjangoMigrationStatistics(Metric):
    """
    Count the number of applied Django migrations per app and sort by
    descending count and ascending app name.
    """
    label = _('Migration Statistics')
    slug = 'django-migration-statistics'
    ordering = '-2.1'
    sql = '''
        SELECT
            app, count(*)
        FROM
            django_migrations
        GROUP BY
            app
        {ORDER_BY}
        ;
    '''


registry.register(DjangoMigrationStatistics)

description

Don’t define this value directly. Instead define a docstring on the metric class.

The docstring will be processed by Python internals to trim leading white spaces and fix newlines. '\r\n' and '\r' line breaks will be normalized to '\n'. Two or more consecutive occurances of '\n' mark a paragraph which will be escaped and wrapped in <p></p> HTML tags. Further, each paragraph will call into Django’s urlize() method to create <a></a> HTML tags around links.

full_sql

The sql formatted with get_order_by_clause().

get_data()

Iterate over all configured PostgreSQL database and execute the full_sql there.

Returns:Returns a list of MetricResult instances. Return type:list

get_order_by_clause()

Turn an ordering string like 1.5.-3.-2.6 into the respective SQL.

SQL’s column numbering starts at 1, so do we here. Given self.ordering as 1.5.-3.-2.6 return a string ORDER BY 1 ASC, 5 ASC, 3 DESC, 2 DESC, 6 ASC.

Ensures that each column (excluding the - prefix) is an integer by calling int() on it.

get_record_item_style(record, item, index)

Given a single record from MetricResult, the value of the current item within, and the current item’s index, decide how to style it. Most likely to be used with the template tag record_item_style().

By default, django-postgres-metrics supports for styling classes:

• ok
• warning
• critical
• info

Override this method and return one of the above strings or None to apply the given style to the entire record. In the Django Admin this will highlight the entire row.

get_record_style(record)

Given a single record from MetricResult, decide how to style it. Most likely to be used with the template tag record_style().

By default, django-postgres-metrics supports for styling classes:

• ok
• warning
• critical
• info

Override this method and return one of the above strings or None to apply the given style to the entire record. In the Django Admin this will highlight the entire row.

label = ''

The label is what is used in the Django Admin views. Consider marking this string as translateable.

ordering = ''

The default ordering that should be applied to the SQL query by default. This needs to be a valid ordering string as defined on parsed_ordering.

parsed_ordering

Turn an ordering string like 1.5.-3.-2.6 into the respective abstraction.

Given self.ordering as 1.5.-3.-2.6 return a lis of 2-tuples like [('', 1), ('', 5), ('-', 3), ('-', 2), ('', 6)].

slug = ''

A URL safe representation of the label and unique across all metrics.

sql = ''

The actual SQL statement that is being used to query the database. In order to make use of the ordering, include the string {ORDER_BY} in the query as necessary. For details on that value see get_order_by_clause().

class postgres_metrics.metrics.MetricResult(connection, records)

Bases: object

Hold a metric’s data for a single database.

alias

The alias under which a database connection is known to Django.

dsn

The PostgreSQL connection string per psycopg2.

records

The rows returned by a metric for the given database.

class postgres_metrics.metrics.MetricHeader(name, index, ordering)

Bases: object

A single column header; mostly takes care of a column’s sorting status.

ascending

True if the column is in ascending order False otherwise

static join_ordering(ordering)

sort_priority

The priority of the columns order. 1 (high), n(low). Default 0.

url_primary

Querystring value making this the primary sorting header.

url_remove

Querystring value removing this column from sorting.

url_toggle

Querystring value toggling ascending/descending for this header.

class postgres_metrics.metrics.AvailableExtensions

PostgreSQL can be extended by installing extensions with the CREATE EXTENSION command. The list of available extensions on each database is shown below.

class postgres_metrics.metrics.CacheHitsMetric

The typical rule for most applications is that only a fraction of its data is regularly accessed. As with many other things data can tend to follow the 80/20 rule with 20% of your data accounting for 80% of the reads and often times its higher than this. Postgres itself actually tracks access patterns of your data and will on its own keep frequently accessed data in cache. Generally you want your database to have a cache hit rate of about 99%.

(Source: http://www.craigkerstiens.com/2012/10/01/understanding-postgres-performance/)

class postgres_metrics.metrics.IndexSizeMetric

class postgres_metrics.metrics.IndexUsageMetric

While there is no perfect answer, if you’re not somewhere around 99% on any table over 10,000 rows you may want to consider adding an index. When examining where to add an index you should look at what kind of queries you’re running. Generally you’ll want to add indexes where you’re looking up by some other id or on values that you’re commonly filtering on such as created_at fields.

(Source: http://www.craigkerstiens.com/2012/10/01/understanding-postgres-performance/)

class postgres_metrics.metrics.TableSizeMetric