Comparison: Oracle vs PostgreSQL

Modified date: Monday, June 30, 2025

Introduction
General
Data Types
SQL
Storage and System
Benchmarking
Tools
Export Regulations
Internal
Internal - Optimizer
Internal - Runtime
Internal - Storage Engine

General

Feature	Oracle	PostgreSQL	Definition
intro	Oracle Database is a DBMS developed by Oracle Corporation.	PostgreSQL is a powerful, open source object-relational database system with over 35 years of active development that has earned it a strong reputation for reliability, feature robustness, and performance.	in their own words - but I reserved the rights to remove some bold claims like "the best", unless it is widely recognized.
vendor	Oracle	PostgreSQL Committees
initial release	1980	1998
latested version	23ai	17	We don't put a release date here as the software is patching frequently. So tracking it is not much useful.
supported platforms	Windows, Linux, Solaris, HP-UX, AIX, z/OS	x86, PowerPC, S/390, SPARC, ARM, MIPS, RISC-V, and PA-RISC	supported OS/CPU platforms
db-engines ranking	1	4	ranks from https://db-engines.com/en/ranking (06/25)
relational?	yes Oracle also has an open source nosql database.	yes	Is it a relational database? (1) Most database are actually with some extensions, for example, nested data types, graph support, etc, which we usually called "multi-model". (2) Some of them are product family, meaning they have more than one database. Here we focus on the main one but explain others when needed.
open source?	no	yes	mainly the engine code
license	commercial	PostgreSQL PostgreSQL is released under the PostgreSQL License, a liberal Open Source license, similar to the BSD or MIT licenses -- allows for commercial use and modification of the software.
on-premise offering	yes	yes	if no means you can't buy "box" software from them
cloud offering	Oracle Cloud and other cloud vendors	cloud vendors PostgreSQL’s cloud offerings are diverse, with many managed services available across major providers. For example, Amazon RDS for PostgreSQL. Technically, there are many efforts on improving PostgreSQL's native cloud implementation. The most famous one is Neon, which is acquired by DataBricks on 2025.
technical doc	https://docs.oracle.com/en/database/	www.postgresql.org/docs
price: box software		0 free download

Data Types

Feature	Oracle	PostgreSQL	Definition
int: 4-bytes int name	int	int
char(n): max bytes	2000	10,485,760
BLOB: max size	(4B-1) * pages Page size is defined by DB_BLOCK_SIZE in Oracle, which is ranging from 2K to 32K. This gives BLOB size from 8T to 128TB.
JSON: max size	32MB
Literal: max size	4000		characters or numbers in SQL or PL/SQL
int: signess		signed only	if differentiate signed and unsigned int
int: 1-bytes int name		n.a.
int: 2-bytes int name		smallint
int: 3-bytes int name		n.a.
int: 8-bytes int name		bigint
decimal: storage size		variable
decimal: range		up to 131072 digits before the decimal point; up to 16383 digits after the decimal point	also called number, numeric in different systems
text: max bytes		1G

SQL

Feature	Oracle	PostgreSQL	Definition
SQL: standard complaince	high	high
max SQL length	undefined The actual limit may depends on limits of the SUT, for example, its memory/system swap settings: Oracle internally must use a malloc'ed buffer to hold the SQL string.	undefined The actual limit may depends on limits of the SUT, for example, its memory/system swap settings: PostgreSQL internally use a struct named "StringInfo" to hold the SQL string, which is with MAX_INT length.	maximal SQL statement length
PL: main	SQL + PL/SQL	SQL + PL/PgSQL	main programming lanage: most database suports SQL because SQL is a well established standard. However, each database would like to extend SQL more or less.
PL: other language support	yes	yes	PL lanaguage other than PL/SQL, like PL/Java, PL/Rust etc
SQL: query hints	complete	GUC only	if it allows use query hints to guide the optimizer
SQL: explicit locking	yes	yes: row, page, table level	Locking is usually an internal matter - so does it allow explicit locking? What levels do they support?
Triggers?	yes	yes	If support triggers
Object-Relational?	some	yes
SP: max parameters		100
UDF: max parameters		100
SQL: max parameters		65535	number of parameters in a PREPARED query
Triggers: scope		tables, views, foreign tables	What objects can have triggers
Triggers: type		BEFORE, AFTER, INSTEAD OF	Types of triggers supported
Extension Mechanism		C programming, link with engine
vector search		no native Extensions like pgvector supports it.	does it support vector search

Storage and System

Feature	Oracle	PostgreSQL	Definition
arch: server	C/S Oracle has a family of databases, even with nonsql one.	C/S	Embedded or traditional C/S?
arch: run in browser?	no	no/yes Officially not supported, but there are some good OSS projects like Pglite.	It also known as a client-side database, is a database that is stored and managed within a user's web browser, rather than on a remote server.
arch: clustering/HA	RAC, Data Guard
arch: in-memory support	Oracle Database In-Memory option	no
arch: Multi-master support?	yes	no	if multi-master support?
arch: primary/read replica?	yes	yes	if primary + mulitiple read replica supported
replication: sync/async	both	both	Can commits wait or w/o wait for replicas to acknowledge
replication: WAL shipping	yes	yes	Uses write-ahead log (WAL) shipping for replication
sessions: max	262143
tables: max number per database	undefined	1,431,650,303
tables: max number of columns	4096		Max number of columns per table
contraints: max per column	undefined
partitions: methods	Range, List, Hash, Composite (sub-partitions supported).	Range, List, Hash; limited composite (multi-level partitioning more limited than Oracle/SQL Server).	Supported partitioning strategies (range, list, hash, etc.).
partitions: global index	yes	no	index across partitions
constraints: max per database	4,294,967,293
rows: max rows per table	undefined	32T/row_size	The actual number depends on storage etc
index: max allowed index	undefined	rows per table is restricted by the number of rows that can fit onto MAX_UINT*8K pages.	Max number of indices allowed per table
index: max allowable size	6400		Max index record size (bytes). This constraint is mainly coming from the fact of the database page size: if we exclude blob data types, database engine usally do not allow a record expand more than one page.
index: max number of fields	32		Max number of columns allowed in one index
partition: max allowed partitions	1M-1		Meta data challenge: 1M partitions just like 1M tables, system have to hold them in memory. Optimizer challenge: O(N) algorithm may lead to very long planning time if there are excessive partitions.
partition: max allowed key columns	16
partition: max number of subpartitions	1M-1
ACID	yes/yes	yes/yes	for DML and DDL
ACID: max isolation level	SI The Snapshot Isolation (SI) implemented by Oracle allows some anomalies, including write skew. But the SI does satisfies ANSI's serializable definition.	Serializable PostgreSQL implements Serializable Snapshot Isolation (SSI) in version 9.1.
ACID: max ANSI isolation level	Serializable	Serializable
ACID: durability	yes	yes
Materialized View: support?	yes	yes
replication: quorum-based commit		no	Multiple synchronous replicas with quorum for commit
database: max number		4,294,950,911 Note that 4G-4294950911=16385. The reason is that a database needs assign an object ID (you see the db folder is a number), which is starting from 16385 because smaller are reserved by boostrap.

Benchmarking

Feature	Oracle	PostgreSQL	Definition
any official TPC benchmarks?	yes	no	The TPC benchmark includes a set of tests simulating real-world scenarios to evaluate database performance.
TPCC: most recent tpmC	8,552,523 System cost: 4,663,073 USD
TPCC: most recent submit date	3/26/2013
TPCC: most recent per thread perf	8352
TPCC: best tpmC	30,249,688 System cost: 30,528,863 USD
TPCC: best perf submit date	12/2/2010
TPCC: best perf per thread perf	2188

Tools

Feature	Oracle	PostgreSQL	Definition
command line client		psql	it means "sql client" for database supporting SQL. For embedded atabase, the client includes the server together.
admin(GUI)		pgAdmin

Export Regulations

Feature	Oracle	PostgreSQL	Definition
Jurisdiction	US	US	Which country controls export
ECCN	5D992.c	None	An Export Control Classification Number (ECCN) is a five-character alphanumeric code used to categorize items on the Commerce Control List (CCL) for export control purposes. Most database may fall into 5D992.c category, "mass market encryption", which means it has some ordinary encryption related code, for example, the SSL connection code.
Eligible License Exception / CCATS	NLR NLR essentially means that a commodity has been classified within the Commodity Classification Automated Tracking System and determined to not require a BIS export license for its export.	Not required There is no ECCN for open source software	A License Exception is an authorization that allows you to export or reexport items subject to the EAR without needing to obtain a specific export license, provided certain conditions are met. CCATS stands for Commodity Classification Automated Tracking System. The BIS assigns a CCATS number to products that it has classified under the Commerce Control List (CCL).
Encryption Components	TDE, SSL	SSL	Crypto functionality that triggers control

Internal

Feature	Oracle	PostgreSQL	Definition
concurrency control	MVCC	MVCC
MVCC: implemented?	yes	yes	if implement MVCC for concurrency control
MVCC: rollback segment	yes	no PostgreSQL uses VACUUM to clean up old versions: it is more difficult than in-memory database because the old versions are mixed with new versions on database pages.	if uses rollback segment (RS) to store old versions. Without RS, old versions and new versions are mixed stored, then the database engine has to find a way to efficiently drop the old versions at certain point.
Implementation language	C	C	A DBMS may use mulitple programming languages, for example, supports its stored procedure. The major programming language used to implement the engine.

Internal - Optimizer

Feature	Oracle	PostgreSQL	Definition
CBO?	yes	yes	if it employees a cost based optimizer
framework	System-R	System-R	System-R is more like a dynamic programming, bottom up optimizer, while Cascades/Volcano gebaseerd optimizer is more like top-down optimizer.
query hints?	complete	GUC only	if it allows use query hints to guide the optimizer
join order search		dynamic programming + Generic Algorithm (GEQO) It also allows to extend the join order algorithm.	How join order permutations are explored during plan generation.
stats: multi column		yes	Multi-column stats may cause storage space bloat: for example, if one dimension has 100 buckets, then three dimensions will require 1M buckets - but reducing the total number of buckets will result in reduced accuracy.
plan guide?		no	Can we use plan guide to correct the plan? This is a more systematic and accurate way to repair the plan than plan hints. Especially during system upgrades, if the plan becomes worse, we can use plan guide to force a query to use a previous plan.

Internal - Runtime

Feature	Oracle	PostgreSQL	Definition
resource management	complete	simple: work_mem controls per-operator memory use	How execution memory is allocated and limited.
support intra-parallel query?	yes	yes	meaning a single query can utilize multi hardware threads to run it
vectorization	yes	no native Several extensions allowed it. For example, pg_duckdb and Hydra.	Speed up OLAP queries using vectorized execution. A vectorized runtime exchange a bunch of rows between iterators, and these rows are physically sotre with column-oriented order.
iterator: join methods	all 3	all 3	Hash Join (HJ), Sort-Merge Join (MJ) and Nested loop Join (NLJ) are 3 major ones
spilling support		yes	"spilling" refers to the process of writing temporary data or intermediate results of a query to disk when the available memory is exhausted. This is crucial for handling large datasets or complex queries that require more memory than available.
model		Volcano + push for parallel run	The operator scheduling model: pull-gebaseerd (Volcano), push etc.
adaptive execution (AQP)?		no	Traditionally, after the optimizer determines the plan, the runtime must execute it completely without any room for adjustment, such as which of the two tables should be built. The adaptive method allows the runtime to make some adjustments based on the actual situation, and the optimizer must also prepare for this uncertainty, such as preparing an alternative plan.
Error: out-of-range and overflow		abort the transaction	To maintain atomic requirement of ACID, database engine usually fail the statement and abort the transaction.

Internal - Storage Engine

Feature	Oracle	PostgreSQL	Definition
Page Size	2K-32K	8K default configurable with the --with-blocksize=BLOCKSIZE option	The physical disk block size for storage and I/O.
partition table	complete	declarative partition table is implemented via inheritance table, since V11	Partitioning capabilities for large tables.
partition table: prunning	both	mostly at compile time, some runtime	Ability to eliminate partitions at query compile time and runtime
ACID: durability mechanism	WAL	WAL	How is it implements durability. Database's classic way is write ahead logging (WAL).
Storage Compression		TOAST compression (within a row)
Row Overflow / Large Row Handling		Row within a page and large columns pointing to TOAST storage	How rows larger than page size are handled. Usually a row must be within one page, but big columns can only save a pointer with the row and pointing to the actual storage. This is also why there is a limit of maximal columns per table.
Index: primary cluster		Heap storage by default; CLUSTER command for static clustering - if modification happens after, order is not maintained.	Whether physical rows are ordered by primary index.
Index: secondary		B+Tree, GIN, GiST, SP-GiST, BRIN, Hash, Fulltext (via extensions).	Supported index types beyond the primary key.
index: column store as primary		No native support; available via extensions (e.g. cstore_fdw, citus).	if column-store as primary storage supported
index: column store as secondary		No native support; available via extensions (e.g. cstore_fdw, citus).	if column-store as secondary index supported

Comparison: Oracle vs PostgreSQL

Table of Contents

General

Data Types

SQL

Storage and System

Benchmarking

Tools

Export Regulations

Internal

Internal - Optimizer

Internal - Runtime

Internal - Storage Engine