Appendix K. PostgreSQL Limits

Appendix K. PostgreSQL Limits
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+ Table K.1 describes various hard limits of + PostgreSQL. However, practical limits, such as + performance limitations or available disk space may apply before absolute + hard limits are reached. +

Table K.1. PostgreSQL Limitations

Item	Upper Limit	Comment
database size	unlimited
number of databases	4,294,950,911
relations per database	1,431,650,303
relation size	32 TB	with the default `BLCKSZ` of 8192 bytes
rows per table	limited by the number of tuples that can fit onto 4,294,967,295 pages
columns per table	1600	further limited by tuple size fitting on a single page; see note + below
columns in a result set	1664
field size	1 GB
identifier length	63 bytes	can be increased by recompiling PostgreSQL
indexes per table	unlimited	constrained by maximum relations per database
columns per index	32	can be increased by recompiling PostgreSQL
partition keys	32	can be increased by recompiling PostgreSQL

+ The maximum number of columns for a table is further reduced as the tuple + being stored must fit in a single 8192-byte heap page. For example, + excluding the tuple header, a tuple made up of 1600 int columns + would consume 6400 bytes and could be stored in a heap page, but a tuple of + 1600 bigint columns would consume 12800 bytes and would + therefore not fit inside a heap page. + Variable-length fields of + types such as text, varchar, and char + can have their values stored out of line in the table's TOAST table when the + values are large enough to require it. Only an 18-byte pointer must remain + inside the tuple in the table's heap. For shorter length variable-length + fields, either a 4-byte or 1-byte field header is used and the value is + stored inside the heap tuple. +

+ Columns that have been dropped from the table also contribute to the maximum + column limit. Moreover, although the dropped column values for newly + created tuples are internally marked as null in the tuple's null bitmap, the + null bitmap also occupies space. +

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