NGSIPostgreSQLSink
Content:
- Functionality
- Administration guide
- Programmers guide
Functionality
com.iot.telefonica.cygnus.sinks.NGSIPostgreSQLSink
, or simply NGSIPostgreSQLSink
is a sink designed to persist NGSI-like context data events within a PostgreSQL server. Usually, such a context data is notified by a Orion Context Broker instance, but could be any other system speaking the NGSI language.
Independently of the data generator, NGSI context data is always transformed into internal NGSIEvent
objects at Cygnus sources. In the end, the information within these events must be mapped into specific PostgreSQL data structures.
Next sections will explain this in detail.
Mapping NGSI events to NGSIEvent
objects
Notified NGSI events (containing context data) are transformed into NGSIEvent
objects (for each context element a NGSIEvent
is created; such an event is a mix of certain headers and a ContextElement
object), independently of the NGSI data generator or the final backend where it is persisted.
This is done at the cygnus-ngsi Http listeners (in Flume jergon, sources) thanks to NGSIRestHandler
. Once translated, the data (now, as NGSIEvent
objects) is put into the internal channels for future consumption (see next section).
Mapping NGSIEvent
s to PostgreSQL data structures
PostgreSQL organizes the data in schemas inside a database that contain tables of data rows. Such organization is exploited by NGSIPostgreSQLSink
each time a NGSIEvent
is going to be persisted.
PostgreSQL databases naming conventions
Previous to any operation with PostgreSQL you need to create the database to be used.
It must be said PostgreSQL only accepts alphanumeric characters and the underscore (_
). This leads to certain encoding is applied depending on the enable_encoding
configuration parameter.
PostgreSQL databases name length is limited to 63 characters.
Since version 2.2.0 It's added a new capability for Cygnus to create the schema and database name on runtime, this is possible trough enabling a specific Data Model on agent properties. That works the following way.
- Data model by entity database (
data_model=dm-by-entity-database
). For this datamodel the name of the database will be auto generated by the sink, this name will be thefiware-service
found on the headers of the first request incoming to the sink. In case there is a database specified on the agent properties, it's ignored. - Data model by entity database schema (
data_model=dm-by-entity-database-schema
). For this datamodel the name of the database will be auto generated by the sink, this name will be thefiware-service
found on the headers of the first request incoming to the sink. In case there is a database specified on the agent properties, it's ignored.
PostgreSQL schemas naming conventions
A schema named as the notified fiware-service
header value (or, in absence of such a header, the defaulted value for the FIWARE service) is created (if not existing yet).
It must be said PostgreSQL only accepts alphanumeric characters and the underscore (_
). This leads to certain encoding is applied depending on the enable_encoding
configuration parameter.
PostgreSQL schemas name length is limited to 63 characters.
Since version 2.2.0 Cygnus creates the name of the schema name on runtime according to the selected DataModel for the sink.
-
Data model by entity database schema (
data_model=dm-by-entity-database-schema
). For this datamodel the name of the schema will be auto generated by the sink, this name will be thefiware-servicePath
found on the headers of the first request to store. -
All the other data models will take the name of the schema from the notified
fiware-service
as usual.
PostgreSQL tables naming conventions
The name of these tables depends on the configured data model (see the Configuration section for more details):
- Data model by service path (
data_model=dm-by-service-path
). As the data model name denotes, the notified FIWARE service path (or the configured one as default inNGSIRestHandler
) is used as the name of the table. This allows the data about all the NGSI entities belonging to the same service path is stored in this unique table. The only constraint regarding this data model is the FIWARE service path cannot be the root one (/
). - Data model by entity (
data_model=dm-by-entity
). For each entity, the notified/default FIWARE service path is concatenated to the notified entity ID and type in order to compose the table name. If the FIWARE service path is the root one (/
) then only the entity ID and type are concatenated. - Data model by entity database schema (
data_model=dm-by-entity-database-schema
). Same as Data model by entity (data_model=dm-by-entity
). - Data model by entity database schema (
data_model=dm-by-entity-database
). Same as Data model by entity (data_model=dm-by-entity
). - Data model by entity type (
data_model=dm-by-entity-type
). For each entity, the notified/default FIWARE service path is concatenated to the notified entity type in order to compose the table name. The concatenation character is_
(underscore). If the FIWARE service path is the root one (/
) then only the entity type is concatenated.
It must be said PostgreSQL only accepts alphanumeric characters and the underscore (_
). This leads to certain encoding is applied depending on the enable_encoding
configuration parameter.
PostgreSQL tables name length is limited to 63 characters.
The following table summarizes the table name composition (old encoding):
FIWARE service path | dm-by-service-path |
dm-by-entity , dm-by-entity-database-schema , dm-by-entity-database |
dm-by-entity-type |
---|---|---|---|
/ |
N/A | <entityId>_<entityType> |
<entityType> |
/<svcPath> |
<svcPath> |
<svcPath>_<entityId>_<entityType> |
<svcPath>_<entityType> |
Using the new encoding:
FIWARE service path | dm-by-service-path |
dm-by-entity , dm-by-entity-database-schema , dm-by-entity-database |
dm-by-entity-type |
---|---|---|---|
/ |
x002f |
x002fxffff<entityId>xffff<entityType> |
x002fxffff<entityType> |
/<svcPath> |
x002f<svcPath> |
x002f<svcPath>xffff<entityId>xffff<entityType> |
x002f<svcPath>xffff<entityType> |
Please observe the concatenation of entity ID and type is already given in the notified_entities
/grouped_entities
header values (depending on using or not the grouping rules, see the Configuration section for more details) within the NGSIEvent
.
Row-like storing
Regarding the specific data stored within the above table, if attr_persistence
parameter is set to row
(default storing mode) then the notified data is stored attribute by attribute, composing an insert for each one of them. Each insert contains the following fields:
recvTimeTs
: UTC timestamp expressed in miliseconds.recvTime
: UTC timestamp in human-redable format (ISO 8601).fiwareServicePath
: Notified fiware-servicePath, or the default configured one if not notified.entityId
: Notified entity identifier.entityType
: Notified entity type.attrName
: Notified attribute name.attrType
: Notified attribute type.attrValue
: In its simplest form, this value is just a string, but since Orion 0.11.0 it can be Json object or Json array.attrMd
: It contains a string serialization of the metadata array for the attribute in Json (if the attribute hasn't metadata, an empty array[]
is inserted). Will be stored only if it was configured to (attr_metadata_store set to true in the configuration file ngsi_agent.conf). It is a Json object.
Column-like storing
Regarding the specific data stored within the above table, if attr_persistence
parameter is set to column
then a single line is composed for the whole notified entity, containing the following fields:
recvTime
: UTC timestamp in human-redable format (ISO 8601).fiwareServicePath
: The notified one or the default one.entityId
: Notified entity identifier.entityType
: Notified entity type.- For each notified attribute, a field named as the attribute is considered. This field will store the attribute values along the time.
- For each notified attribute, a field named as the concatenation of the attribute name and
_md
is considered. This field will store the attribute's metadata values along the time.
Native attribute type
Regarding the specific data stored within the above table, if attr_native_types
parameter is set to true
then attribute is inserted using its native type (according with the following table), if false
then will be stringify.
Type json | Type PostGreSQL/POSTGIS |
---|---|
string | text |
number | double, precision, real, others (numeric, decimal) |
boolean | boolean (TRUE, FALSE, NULL) |
DateTime | timestamp, timestamp with time zone, timestamp without time zone |
json | text o json - it`s treated as String |
null | NULL |
This only applies to Column mode.
Example
NGSIEvent
Assuming the following NGSIEvent
is created from a notified NGSI context data (the code below is an object representation, not any real data format):
ngsi-event={
headers={
content-type=application/json,
timestamp=1429535775,
transactionId=1429535775-308-0000000000,
correlationId=1429535775-308-0000000000,
fiware-service=vehicles,
fiware-servicepath=/4wheels,
<grouping_rules_interceptor_headers>,
<name_mappings_interceptor_headers>
},
body={
entityId=car1,
entityType=car,
attributes=[
{
attrName=speed,
attrType=float,
attrValue=112.9
},
{
attrName=oil_level,
attrType=float,
attrValue=74.6
}
]
}
}
Database, schema and table names
The PostgreSQL database name will be of the user's choice.
The PostgreSQL schema will always be vehicles
.
The PostgreSQL table names will be, depending on the configured data model, the following ones (old encoding):
FIWARE service path | dm-by-service-path |
dm-by-entity |
dm-by-entity-type |
---|---|---|---|
/ |
N/A | car1_car |
car |
/4wheels |
4wheels |
4wheels_car1_car |
4wheels_car |
Using the new encoding:
FIWARE service path | dm-by-service-path |
dm-by-entity |
dm-by-entity |
---|---|---|---|
/ |
x002f |
x002fxffffcar1xffffcar |
x002fxffffcar |
/wheels |
x002f4wheels |
x002f4wheelsxffffcar1xffffcar |
x002f4wheelsxffffcar |
Row-like storing
Assuming attr_persistence=row
as configuration parameters, then NGSIPostgreSQLSink
will persist the data within the body as:
$ psql -U myuser
psql (9.5.0)
Type "help" for help.
postgres-# \c my-database
my-database# \dn
List of schemas
Name | Owner
----------+----------
vehicles | postgres
public | postgres
(2 rows)
my-database=# \dt vehicles.*
List of relations
Schema | Name | Type | Owner
----------+-------------------+-------+----------
vehicles | 4wheels_car1_car | table | postgres
(1 row)
postgresql> select * from vehicles.4wheels_car1_car;
+------------+----------------------------+-------------------+----------+------------+-------------+-----------+-----------+--------+
| recvTimeTs | recvTime | fiwareServicePath | entityId | entityType | attrName | attrType | attrValue | attrMd |
+------------+----------------------------+-------------------+----------+------------+-------------+-----------+-----------+--------+
| 1429535775 | 2015-04-20T12:13:22.41.124 | 4wheels | car1 | car | speed | float | 112.9 | [] |
| 1429535775 | 2015-04-20T12:13:22.41.124 | 4wheels | car1 | car | oil_level | float | 74.6 | [] |
+------------+----------------------------+-------------------+----------+------------+-------------+-----------+-----------+--------+
2 row in set (0.00 sec)
Column-like storing
Coming soon.
Administration guide
Configuration
NGSIPostgreSQLSink
is configured through the following parameters:
Parameter | Mandatory | Default value | Comments |
---|---|---|---|
type | yes | N/A | Must be com.telefonica.iot.cygnus.sinks.NGSIPostgreSQLSink |
channel | yes | N/A | |
enable_encoding | no | false | true or false, true applies the new encoding, false applies the old encoding. |
enable_grouping | no | false | true or false. Check this link for more details. |
enable_name_mappings | no | false | true or false. Check this link for more details. |
enable_lowercase | no | false | true or false. |
enable_last_data | no | false | true or false, to enable last data functionality. Check this link for more details. |
last_data_table_suffix | no | false | This suffix will be added to the table name in order to know where Cygnus will store the last record of an entity. Check this link for more details. |
last_data_unique_key | no | entityId | This must be a unique key on the database to find when a previous record exists. Check this link for more details. |
last_data_timestamp_key | no | recvTime | This must be a timestamp key on the aggregation to know which record is older. Check this link for more details. |
last_data_sql_timestamp_format | no | YYYY-MM-DD HH24:MI:SS.MS | This must be a timestamp format to cast SQL Text to timestamp. Check this link for more details. |
data_model | no | dm-by-entity | dm-by-service-path or dm-by-entity or dm-by-entity-type or dm-by-entity-database or dm-by-entity-database-schema. dm-by-service and |
postgresql_host | no | localhost | FQDN/IP address where the PostgreSQL server runs. |
postgresql_port | no | 5432 | |
postgresql_database | no | postgres | postgres is the default database that is created automatically when install. Note also than with datamodels dm-by-entity-database and dm-by-entity-database-schema this setting is ignored (as the database is part of the mapping done by the datamodel) |
postgresql_username | no | postgres | postgres is the default username that is created automatically when install |
postgresql_password | no | N/A | Empty value by default (No password is created when install) |
postgresql_options | no | N/A | optional connection parameter(s) concatinated to jdbc url if necessary When sslmode=require is set to postgresql_options , jdbc url will become like jdbc:postgresql://postgresql.example.com:5432/postgres?sslmode=require |
attr_persistence | no | row | row or column. |
attr_metadata_store | no | false | true or false. |
attr_native_types | no | false | if the attribute value will be native true or stringfy or false. |
batch_size | no | 1 | Number of events accumulated before persistence. |
batch_timeout | no | 30 | Number of seconds the batch will be building before it is persisted as it is. |
batch_ttl | no | 10 | Number of retries when a batch cannot be persisted. Use 0 for no retries, -1 for infinite retries. Please, consider an infinite TTL (even a very large one) may consume all the sink's channel capacity very quickly. |
batch_retry_intervals | no | 5000 | Comma-separated list of intervals (in miliseconds) at which the retries regarding not persisted batches will be done. First retry will be done as many miliseconds after as the first value, then the second retry will be done as many miliseconds after as second value, and so on. If the batch_ttl is greater than the number of intervals, the last interval is repeated. |
backend.enable_cache | no | false | true or false, true enables the creation of a Cache, false disables the creation of a Cache. |
persist_errors | no | true | if there is an exception when trying to persist data into storage then error is persisted into a table |
A configuration example could be:
cygnus-ngsi.sinks = postgresql-sink
cygnus-ngsi.channels = postgresql-channel
...
cygnus-ngsi.sinks.postgresql-sink.type = com.telefonica.iot.cygnus.sinks.NGSIPostgreSQLSink
cygnus-ngsi.sinks.postgresql-sink.channel = postgresql-channel
cygnus-ngsi.sinks.postgresql-sink.enable_encoding = false
cygnus-ngsi.sinks.postgresql-sink.enable_grouping = false
cygnus-ngsi.sinks.postgresql-sink.enable_lowercase = false
cygnus-ngsi.sinks.postgresql-sink.enable_name_mappings = false
cygnus-ngsi.sinks.postgresql-sink.data_model = dm-by-entity
cygnus-ngsi.sinks.postgresql-sink.postgresql_host = 192.168.80.34
cygnus-ngsi.sinks.postgresql-sink.postgresql_port = 5432
cygnus-ngsi.sinks.postgresql-sink.postgresql_database = mydatabase
cygnus-ngsi.sinks.postgresql-sink.postgresql_username = myuser
cygnus-ngsi.sinks.postgresql-sink.postgresql_password = mypassword
cygnus-ngsi.sinks.postgresql-sink.postgresql_options = sslmode=require
cygnus-ngsi.sinks.postgresql-sink.attr_persistence = row
cygnus-ngsi.sinks.postgresql-sink.attr_native_types = false
cygnus-ngsi.sinks.postgresql-sink.batch_size = 100
cygnus-ngsi.sinks.postgresql-sink.batch_timeout = 30
cygnus-ngsi.sinks.postgresql-sink.batch_ttl = 10
cygnus-ngsi.sinks.postgresql-sink.batch_retry_intervals = 5000
cygnus-ngsi.sinks.postgresql.backend.enable_cache = false
cygnus-ngsi.sinks.postgresql-sink.persist_errors = true
Use cases
Use NGSIPostgreSQLSink
if you are looking for a big database with several tenants. PostgreSQL is bad at having several databases, but very good at having different schemas.
Important notes
About the table type and its relation with the grouping rules
The table type configuration parameter, as seen, is a method for direct aggregation of data: by default destination (i.e. all the notifications about the same entity will be stored within the same PostgreSQL table) or by default service-path (i.e. all the notifications about the same service-path will be stored within the same PostgreSQL table).
The Grouping feature is another aggregation mechanism, but an inderect one. This means the grouping feature does not really aggregates the data into a single table, that's something the sink will done based on the configured table type (see above), but modifies the default destination or service-path, causing the data is finally aggregated (or not) depending on the table type.
For instance, if the chosen table type is by destination and the grouping feature is not enabled then two different entities data, car1
and car2
both of type car
will be persisted in two different PostgreSQL tables, according to their default destination, i.e. car1_car
and car2_car
, respectively. However, if a grouping rule saying "all cars of type car
will have a modified destination named cars
" is enabled then both entities data will be persisted in a single table named cars
. In this example, the direct aggregation is determined by the table type (by destination), but indirectly we have been deciding the aggregation as well through a grouping rule.
About the persistence mode
Please observe not always the same number of attributes is notified; this depends on the subscription made to the NGSI-like sender. This is not a problem for the row
persistence mode, since fixed 8-fields data rows are inserted for each notified attribute. Nevertheless, the column
mode may be affected by several data rows of different lengths (in term of fields). Thus, the column
mode is only recommended if your subscription is designed for always sending the same attributes, event if they were not updated since the last notification.
In addition, when running in column
mode, due to the number of notified attributes (and therefore the number of fields to be written within the Datastore) is unknown by Cygnus, the table can not be automatically created, and must be provisioned previously to the Cygnus execution. That's not the case of the row
mode since the number of fields to be written is always constant, independently of the number of notified attributes.
About batching
As explained in the programmers guide, NGSIPostgreSQLSink
extends NGSISink
, which provides a built-in mechanism for collecting events from the internal Flume channel. This mechanism allows extending classes have only to deal with the persistence details of such a batch of events in the final backend.
What is important regarding the batch mechanism is it largely increases the performance of the sink, because the number of writes is dramatically reduced. Let's see an example, let's assume a batch of 100 NGSIEvent
s. In the best case, all these events regard to the same entity, which means all the data within them will be persisted in the same PostgreSQL table. If processing the events one by one, we would need 100 inserts into PostgreSQL; nevertheless, in this example only one insert is required. Obviously, not all the events will always regard to the same unique entity, and many entities may be involved within a batch. But that's not a problem, since several sub-batches of events are created within a batch, one sub-batch per final destination PostgreSQL table. In the worst case, the whole 100 entities will be about 100 different entities (100 different PostgreSQL tables), but that will not be the usual scenario. Thus, assuming a realistic number of 10-15 sub-batches per batch, we are replacing the 100 inserts of the event by event approach with only 10-15 inserts.
The batch mechanism adds an accumulation timeout to prevent the sink stays in an eternal state of batch building when no new data arrives. If such a timeout is reached, then the batch is persisted as it is.
Regarding the retries of not persisted batches, a couple of parameters is used. On the one hand, a Time-To-Live (TTL) is used, specifing the number of retries Cygnus will do before definitely dropping the event. On the other hand, a list of retry intervals can be configured. Such a list defines the first retry interval, then se second retry interval, and so on; if the TTL is greater than the length of the list, then the last retry interval is repeated as many times as necessary.
By default, NGSIPostgreSQLSink
has a configured batch size and batch accumulation timeout of 1 and 30 seconds, respectively. Nevertheless, as explained above, it is highly recommended to increase at least the batch size for performance purposes. Which are the optimal values? The size of the batch it is closely related to the transaction size of the channel the events are got from (it has no sense the first one is greater then the second one), and it depends on the number of estimated sub-batches as well. The accumulation timeout will depend on how often you want to see new data in the final storage. A deeper discussion on the batches of events and their appropriate sizing may be found in the performance document.
Time zone information
Time zone information is not added in PostgreSQL timestamps since PostgreSQL stores that information as a environment variable. PostgreSQL timestamps are stored in UTC time.
About the encoding
Until version 1.2.0 (included), Cygnus applied a very simple encoding:
- All non alphanumeric characters were replaced by underscore,
_
. - The underscore was used as concatenator character as well.
- The slash,
/
, in the FIWARE service paths is ignored.
From version 1.3.0 (included), Cygnus applies this specific encoding tailored to PostgreSQL data structures:
- Lowercase alphanumeric characters are not encoded.
- Upercase alphanumeric characters are encoded.
- Numeric characters are not encoded.
- Underscore character,
_
, is not encoded. - Equals character,
=
, is encoded asxffff
. - All other characters, including the slash in the FIWARE service paths, are encoded as a
x
character followed by the Unicode of the character. - User defined strings composed of a
x
character and a Unicode are encoded asxx
followed by the Unicode. xffff
is used as concatenator character.
Despite the old encoding will be deprecated in the future, it is possible to switch the encoding type through the enable_encoding
parameter as explained in the configuration section.
Programmers guide
NGSIPostgreSQLSink
class
As any other NGSI-like sink, NGSIPostgreSQLSink
extends the base NGSISink
. The methods that are extended are:
void persistBatch(Batch batch) throws Exception;
A Batch
contains a set of NGSIEvent
objects, which are the result of parsing the notified context data events. Data within the batch is classified by destination, and in the end, a destination specifies the PostgreSQL table where the data is going to be persisted. Thus, each destination is iterated in order to compose a per-destination data string to be persisted thanks to any PostgreSQLBackend
implementation.
public void start();
An implementation of PostgreSQLBackend
is created. This must be done at the start()
method and not in the constructor since the invoking sequence is NGSIPostgreSQLSink()
(contructor), configure()
and start()
.
public void configure(Context);
A complete configuration as the described above is read from the given Context
instance.
Authentication and authorization
Current implementation of NGSIPostgreSQLSink
relies on the database, username and password credentials created at the PostgreSQL endpoint.
SSL/TLS connection
When NGSIPostgreSQLSink
want to connect PostgreSQL Server by using SSL or TLS, please set postgresql_options
configuration parameter to configure jdbc.