The goal of this document is to investigate about the PostgreSQL capability to handle Json documents.
Introduction
PostgreSQL offers two types for storing JSON data: json
and jsonb. T
he json
data type stores an exact copy of the input text, which processing functions must reparse on each execution; while jsonb
data is stored in a decomposed binary format that makes it slightly slower to input due to added conversion overhead, but significantly faster to process, since no reparsing is needed. jsonb
also supports indexing, which can be a significant advantage.
Because the json
type stores an exact copy of the input text, it will preserve semantically-insignificant white space between tokens, as well as the order of keys within JSON objects. Also, if a JSON object within the value contains the same key more than once, all the key/value pairs are kept. (The processing functions consider the last value as the operative one.) By contrast, jsonb
does not preserve white space, does not preserve the order of object keys, and does not keep duplicate object keys. If duplicate keys are specified in the input, only the last value is kept.
Note
Using PostgreSQL special type as "json" or "jsonb" rather than "text", all applications will lose any compatibility with H2 and MariaDB. They will be mentioned in this document but not recommended.
Type | DataStore | Validation | Support Query | Index | Preserve Order |
---|---|---|---|---|---|
longtext | MariaDB | SELECT | Yes | No | Yes |
PostgreSQL | No | No | No | Yes | |
json | PostgreSQL | INSERT / UPDATE | Yes | No | Yes |
jsonb | PostgreSQL | INSERT / UPDATE | Yes | Yes | No |
Requirements
- Policy types/Policies/Node Types/Node Templates are first order items
- Data Types have a scope of a first order item, so a data type definition only applies in the scope of a policy type or node type definition
- We should keep our current APIs, all changes should be internal
- We must provide an upgrade path to the new data structure and a rollback to the current structure
ORM Layer using Document Storage
ORM layer using document storage (PostgreSQL or MongoDB) could be organized in two layer:
- Document layer (Domain Model to be converted in Json) - implementation has no dependency from DB
- Persistence layer - (Domain Model depend of the DB used): Entities for PostgreSQL, Documents for MongoDB
An implementation on the Document layer could be found here: (https://gerrit.nordix.org/c/onap/policy/models/+/13633)
Example
In the example below DocToscaServiceTemplate should be serialized to Json.
In the example below the implementation of JpaToscaServiceTemplate for PostgreSQL/MariaDB
In the example below the implementation of JpaToscaServiceTemplate for MongoDB
Converters
Jakarta and Spring do no support json Type, but we can use Converters to convert DocToscaServiceTemplate to a Json String.
Note: Serialization and deserialization in Json is already used in policy-model (Un example could be found here [JpaToscaPolicy.java]). @Converter is just an elegant way to do the same thing.
ToscaServiceTemplate Table
clampacm=# \d ToscaServiceTemplate
Table "public.toscaservicetemplate"
Column | Type | Collation | Nullable | Default
-----------------+------------------------+-----------+----------+---------
name | character varying(120) | | not null |
version | character varying(20) | | not null |
servicetemplate | text | | |
Indexes:
"toscaservicetemplate_pkey" PRIMARY KEY, btree (name, version)
clampacm=# select * from public.ToscaServiceTemplate;
name | version | servicetemplate
--------------------+---------+-----------------
PMSH_Test_Instance | 1.0.0 | 16505
(1 row)
clampacm=# select convert_from(lo_get(servicetemplate::oid), 'UTF8') from toscaservicetemplate;
{"tosca_definitions_version":"tosca_simple_yaml_1_3", ...
Proposals
The new ORM level should be additional and optional to the existence one. My propose options are shown below:
- Save ToscaServiceTemplace as Json String in a single Entity:
- ToscaServiceTemplace saved in a Text field as Json
- It is compatible with H2, MariaDB and PostgreSQL
- It is an additional code for policy-models and a medium impact for all applications that are using it
- That solution is compatible with not Spring Applications
- MongoDB/Cassandra
- Document oriented approach full supported by SpringBoot (not needs Converters)
- Compatible only with MongoDB/Cassandra (MongoDB and Cassandra are not compatible to each other)
- It is an additional code for policy-models and a huge impact for all applications that are using it (all repositories and persistence classes have to change to a Document oriented classes)
- Unit tests need an Embedded Server (example for cassandra: EmbeddedCassandraServerHelper or CassandraContainer)
- Spring Boot has own annotations for Documents. Eventually for application not in Spring Boot, it needs additional dao style implementation
Note
- Using document storage, it involves only the ORM layer, it does not change the functionality of the application
- After migration to document storage, it will possible to adjust flexibility of Tosca Service Template Handling (POLICY-3236); as new feature it will impact the business logic of the application
Benchmark Performance of runtime-acm
In order to generate the benchmark I have used (into a laptop) a Virtual Machine whit the follow configuration:
- 8192 Mb
- 2 CPU
For the tests:
- Jmeter to generate requests (same used by performance tests)
- Prometheus for monitoring
- DMaap simulator
- Participant simulator
- MariaDB/PostgreSQL/MongoDB
The existing system
Hibernate/Mariadb. Tosca Service template is saved as a schema entity relation.
Using Json in MariaDB
Hibernate/Mariadb. Tosca Service Template is saved into a longtext as Json.
Using Json in Postgres
Hibernate/PostgreSQL. Tosca Service Template is saved into a text type as Json.
MongoDB
MongoDB. Tosca Service Template is saved as MongoDB Document.
id cannot have dot '.' in MongoDB : solved with minimal configuration
Conclusion
- Work in progress