System Table Compatibility

Besides compatibility with the PostgreSQL SQL dialect and protocol, CedarDB also supports a large part of the PostgreSQL system table catalog in the pg_catalog schema. These system tables contain information about the system state in the form of metadata. This metadata is often used by external tools and clients to interact with the database system for introspection and reflection, e.g., to show which tables exist.

This page provides an overview of the currently supported system tables and views.

• 🟢 Supported
• 🟡 Stubbed for compatibility: These do not contain actual content and exist solely for compatibility purposes, as CedarDB does not share PostgreSQL’s codebase or internal architecture
• 🔴 Not yet supported

Additionally, CedarDB exposes information that are not available in PostgreSQL in its CedarDB system tables.

System Tables

System tables provide a raw view into the state of the database system. In contrast to PostgreSQL, system tables in CedarDB are read-only, and can only be indirectly influenced through DDL statements.

System tables often contain many low-level details. For more accessible and friendly access to the same information, consider using the built-in system views, or the SQL-standard information schema.

CedarDB System Tables

CedarDB provides additional information in its system-specific system tables. As the PostgreSQL system tables, those system tables are read-only.

cedardb_compression_info

This system table contains information about how tables and columns are compressed in CedarDB. Note that CedarDB can use different compression schemes within the same column and that this table currently only includes statistics on cold data. For more information on cold and hot data, see this blog post.

This is an excerpt of the output for TPCH with scale factor 1:

oid         tablename   attributename   datatype    encoding                compressedvaluesize compressedsize  uncompressedsize    tuplecount
-----
268435460   partsupp    ps_comment      text        simple dictionary       fourbyte            104230496       107284124           768830
268435460   partsupp    ps_supplycost   numeric     truncate                fourbyte            3075344         6150640             768830
268435460   partsupp    ps_availqty     integer     truncate                twobyte             1537680         3075320             768830
268435460   partsupp    ps_suppkey      integer     truncate                twobyte             1537680         3075320             768830
268435460   partsupp    tid             bigint      increment               zerobytes           0               6150640             768830
268435460   partsupp    ps_partkey      integer     frameofreference        twobyte             1537680         3075320             768830
268435462   orders      tid             bigint      increment               zerobytes           0               12000000            1500000
268435462   orders      o_clerk         char        sortedstring dictionary twobyte             3114096         46495400            1500000
268435462   orders      o_comment       text        simple dictionary       fourbyte            90643872        96751711            1500000
...

System Views

System views provide convenient access to system information. System tables often contain numeric identifiers, e.g., for the owner of tables. The views instead use more human-readable symbolic names.

CedarDB System Views

cedardb_compression_infos

This system view gives an easier usable representation of the compression ratio of the entries in the cedardb_compression_info system table.

Information Schema

The information_schema is a standardized, cross-database schema that allows portable system introspection. For compatibility, CedarDB follows the PostgreSQL Information Schema, which matches the ISO/IEC 9075-11 standard.

select * from information_schema.tables;