NGSIOracleSQLSink

Content:

Functionality

com.iot.telefonica.cygnus.sinks.NGSIOracleSQLSink, or simply NGSIOracleSQLSink is a sink designed to persist NGSI-like context data events within a Oracle server 11g and 12c legacy versions. 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 Oracle data structures.

Next sections will explain this in detail.

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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).

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Mapping NGSIEvents to Oracle data structures

Oracle organizes the data in databases that contain tables of data rows. Such organization is exploited by NGSIOracleSQLSink each time a NGSIEvent is going to be persisted.

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Oracle databases naming conventions

A database 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 Oracle only accepts alphanumerics $, _ and #. This leads to certain encoding is applied depending on the enable_encoding configuration parameter.

Oracle prior version to 12.2 databases name length is limited to 30 characters.

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Oracle 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 in NGSIRestHandler 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. The concatenation character is _ (underscore). If the FIWARE service path is the root one (/) then only the entity ID and type are concatenated.
  • 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 Oracle only accepts alphanumerics $, _ and #. This leads to certain encoding is applied depending on the enable_encoding configuration parameter.

Oracle prior version to 12.2 databases name length is limited to 30 characters.

The following table summarizes the table name composition (old encoding):

FIWARE service path dm-by-service-path dm-by-entity dm-by-entity-type
/ N/A <entityId>_<entityType> <entityType>
/<svcPath> <svcPath> <svcPath>_<entityId>_<entityType> <svcPath>_<entityType>

The following table summarizes the table name composition (new encoding):

FIWARE service path dm-by-service-path dm-by-entity 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 header value within the NGSIEvent.

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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-readable 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.

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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: Timestamp in human-readable format (Similar to ISO 8601, but avoiding the Z character denoting UTC, since all Oracle timestamps are supposed to be in UTC format).
  • 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.

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Native types

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
string varchar, varchar2, clob
number NUMBER(precision, scale)
boolean boolean (TRUE, FALSE, YES, NO, ON, OFF)
DateTime timestamp, timestamp with time zone, timestamp without time zone
json varchar, varchar2, clob - it`s treated as String
null NULL

This only applies to Column mode.

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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,
         <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
            }
        ]
    }
}

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Database and table names

The Oracle database name will always be vehicles.

The Oracle 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

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Row-like storing

Assuming attr_persistence=row as configuration parameter, then NGSIOracleSQLSink will persist the data within the body as:

sqlplus> select * from 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)

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Column-like storing

If attr_persistence=colum then NGSIOracleSQLSink will persist the data within the body as:

sqlplus> select * from 4wheels_car1_car;
+----------------------------+-------------------+----------+------------+-------+----------+-----------+--------------+
| recvTime                   | fiwareServicePath | entityId | entityType | speed | speed_md | oil_level | oil_level_md |
+----------------------------+-------------------+----------+------------+-------+----------+-----------+--------------+
| 2015-04-20T12:13:22.41.124 | 4wheels           | car1     | car        | 112.9 | []       |  74.6     | []           |
+----------------------------+-------------------+----------+------------+-------+----------+-----------+--------------+
1 row in set (0.00 sec)

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Administration guide

Configuration

NGSIOracleSQLSink is configured through the following parameters:

Parameter Mandatory Default value Comments
type yes N/A Must be com.telefonica.iot.cygnus.sinks.NGSIOracleSQLSink
channel yes N/A
enable_encoding  no false true or false, true applies the new encoding, false applies the old encoding.
enable_name_mappings no false true or false. Check this link for more details.
enable_lowercase no false true or false.
last_data_mode no insert insert to set last data mode. Check this link for more details. In oracle sink both and upsert are not avaiable
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, dm-by-entity or dm-by-entity-type. dm-by-service and <dm-by-attribute are not currently supported.
oracle_host no localhost FQDN/IP address where the Oracle server runs
oracle_port no 1521
oracle_username no system system is the default username that is created automatically
oracle_password no oracle oracle is the default for default username
oracle_database no xe xe is the default database avaiable in oracle 11g XE (express edition)
oracle_maxPoolSize no 3 Max number of connections per database pool
oracle_options no N/A optional connection parameter(s) concatinated to jdbc url if necessary
When useSSL=true&requireSSL=false is set to oracle_options, jdbc url will become like jdbc:oracle://oracle.example.com:3306/fiwareservice?useSSL=true&requireSSL=false
attr_persistence no row row or column
attr_metadata_store no false true 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.
persistence_policy.max_records no -1 Maximum number of records allowed for a table before it is capped. -1 disables this policy.
persistence_policy.expiration_time no -1 Maximum number of seconds a record is maintained in a table before expiration. -1 disables this policy.
persistence_policy.checking_time no 3600 Frequency (in seconds) at which the sink checks for record expiration.
attr_native_types no false if the attribute value will be native true or stringfy or false. When set to true, in case batch option is activated, insert null values for those attributes that doesn't exist in some of the entities to be inserted. If set to false, '' value is inserted for missing attributes.
persist_errors no true if there is an exception when trying to persist data into storage then error is persisted into a table
oracle_locator no false if there is avaiable of Oracle locator feature which is just avaible since oracle 12c. THis imples if a geo:json is in converted a SDO_GEOMETRY or just leave in string format.
oracle_major_version no 11 Major version of Oracle (it defines some values like max name length for identifiers, whichs is 30 for versions prior to 12)
nls_timestamp_format no YYYY-MM-DD HH24:MI:SS.FF6 defines the default timestamp format to use with the TO_CHAR and TO_TIMESTAMP functions nls_timestamp_format
nls_timestamp_tz_format no YYYY-MM-DD"T"HH24:MI:SS.FF6 TZR NLS_TIMESTAMP_TZ_FORMAT defines the default timestamp with time zone format to use with the TO_CHAR and TO_TIMESTAMP_TZ functions nls_timestamp_tz_format

A configuration example could be:

cygnus-ngsi.sinks = oracle-sink
cygnus-ngsi.channels = oracle-channel
...
cygnus-ngsi.sinks.oracle-sink.type = com.telefonica.iot.cygnus.sinks.NGSIOracleSQLSink
cygnus-ngsi.sinks.oracle-sink.channel = oracle-channel
cygnus-ngsi.sinks.oracle-sink.enable_encoding = false
cygnus-ngsi.sinks.oracle-sink.enable_lowercase = false
cygnus-ngsi.sinks.oracle-sink.enable_name_mappings = false
cygnus-ngsi.sinks.oracle-sink.data_model = dm-by-entity
cygnus-ngsi.sinks.oracle-sink.oracle_host = 192.168.80.34
cygnus-ngsi.sinks.oracle-sink.oracle_port = 1521
cygnus-ngsi.sinks.oracle-sink.oracle_database = xe
cygnus-ngsi.sinks.oracle-sink.oracle_username = system
cygnus-ngsi.sinks.oracle-sink.oracle_password = oracle
cygnus-ngsi.sinks.oracle-sink.oracle_locator = false
cygnus-ngsi.sinks.oracle-sink.nl_timestamp_format = YYYY-MM-DD HH24:MI:SS.FF6
cygnus-ngsi.sinks.oracle-sink.nl_timestamp_tz_format = YYYY-MM-DD\"T\"HH24:MI:SS.FF6 TZR
cygnus-ngsi.sinks.oracle-sink.oracle_maxPoolSize = 3
cygnus-ngsi.sinks.oracle-sink.attr_persistence = column
cygnus-ngsi.sinks.oracle-sink.attr_native_types = false
cygnus-ngsi.sinks.oracle-sink.batch_size = 100
cygnus-ngsi.sinks.oracle-sink.batch_timeout = 30
cygnus-ngsi.sinks.oracle-sink.batch_ttl = 10
cygnus-ngsi.sinks.oracle-sink.batch_retry_intervals = 5000
cygnus-ngsi.sinks.oracle-sink.persistence_policy.max_records = 5
cygnus-ngsi.sinks.oracle-sink.persistence_policy.expiration_time = 86400
cygnus-ngsi.sinks.oracle-sink.persistence_policy.checking_time = 600
cygnus-ngsi.sinks.oracle-sink.persist_errors = true

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Use cases

Use NGSIOracleSQLSink if you are looking for a database storage not growing so much in the mid-long term.

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Important notes

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.

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About batching

As explained in the programmers guide, NGSIOracleSQLSink 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 NGSIEvents. 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 Oracle table. If processing the events one by one, we would need 100 inserts into Oracle; 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 Oracle table. In the worst case, the whole 100 entities will be about 100 different entities (100 different Oracle 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, NGSIOracleSQLSink 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.

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Time zone information

Timezone in oracle is defiend by NLS_LANG environment variable of database instance. Timestamp and timestampTZ formats are defined by NLS_TIMESTAMP_FORMAT and NLS_TIMESTAMP_TZ_FORMAT environment variables of database instance as well as each connection session. More about time tonze information.

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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 Oracle data structures:

  • Alphanumeric characters are not encoded.
  • Numeric characters are not encoded.
  • Underscore character, _, is not encoded.
  • Equals character, =, is encoded as xffff.
  • 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 as xx followed by the Unicode.
  • All the other characters are not encoded.
  • 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.

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About capping resources and expirating records

Capping and expiration are disabled by default. Nevertheless, if desired, this can be enabled:

  • Capping by the number of records. This allows the resource growing up until certain configured maximum number of records is reached (persistence_policy.max_records), and then maintains such a constant number of records.
  • Expirating by time the records. This allows the resource growing up until records become old, i.e. exceed certain configured expiration time (persistence_policy.expiration_time).

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Programmers guide

NGSIOracleSQLSink class

As any other NGSI-like sink, NGSIOracleSQLSink 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 Oracle 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 OracleBackend implementation.

void capRecords(NGSIBatch batch, long maxRecords) throws EventDeliveryException;

This method is always called immediatelly after persistBacth(). The same destination tables that were upserted are now checked in terms of number of records: if the configured maximum (persistence_policy.max_records) is exceeded for any of the updated tables, then as many oldest records are deleted as required until the maximum number of records is reached.

void expirateRecords(long expirationTime);

This method is called in a periodical way (based on persistence_policy.checking_time), and if the configured expiration time (persistence_policy.expiration_time) is exceeded for any of the records within any of the tables, then it is deleted.

public void start();

An implementation of OracleBackend is created. This must be done at the start() method and not in the constructor since the invoking sequence is NGSIOracleSQLSink() (contructor), configure() and start().

public void configure(Context);

A complete configuration as the described above is read from the given Context instance.

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Authentication and authorization

Current implementation of NGSIOracleSQLSink relies on the username and password credentials created at the Oracle endpoint as well as database name.

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