This topic describes the limits of Apsara PolarDB.

PolarDB MySQL

Node specification Memory occupied by the file system Maximum number of files
polar.mysql.x2.medium 450 MB 1,026,048
polar.mysql.x4.large 850 MB 2,050,048
polar.mysql.x4.xlarge
polar.mysql.x8.xlarge
polar.mysql.x8.2xlarge
polar.mysql.x8.4xlarge
polar.mysql.x8.12xlarge
Description:
  • Maximum number of files
    Includes user files, database system files (approximately 100), and log files. To view the number of log files, run the SHOW POLAR LOGS command. An Apsara PolarDB table occupies two files. A partition table occupies N + 2 files, where N indicates the number of partitions. The following error message appears when you create a table after the maximum number of files is reached: 
    ERROR 3017 (HY000): Too many files. PolarDB only supports 2048 files every 10GB disk size. Please drop some tables/databases before creating new tables

    In this case, you need to delete some tables or upgrade the specifications of your cluster.

  • Memory occupied by the file system

    The amount of memory that is occupied by the file system when your cluster has reached its storage limit and can read and write data normally (neither when the cluster is under performance stress testing nor when you perform DDL operations on large tables). The file system occupies fewer memory resources than the value specified in the table if your cluster has not reached its storage limit.

Table 1. Other limits
Item Limit
Table name The name of a table in a cluster of any specification must be up to 64 letters and digits or 50 Chinese characters in length.
Serializable isolation level Not supported.

PolarDB PostgreSQL

Node specification Maximum number of files
polar.pg.x4.medium 1,048,576
polar.pg.x4.large 2,097,152
polar.pg.x4.xlarge 2,097,152
polar.pg.x8.xlarge 4,194,304
polar.pg.x8.2xlarge 8,388,608
polar.pg.x8.4xlarge 12,582,912
polar.pg.x8.12xlarge 20,971,520
polar.o.x4.medium 1,048,576
polar.o.x4.large 2,097,152
polar.o.x4.xlarge 2,097,152
polar.o.x8.xlarge 4,194,304
polar.o.x8.2xlarge 8,388,608
polar.o.x8.4xlarge 12,582,912
polar.o.x8.12xlarge 20,971,520
Maximum number of files: includes user table files, database system table files (approximately 1,000), and log files. An Apsara PolarDB table (non-partition table) occupies three files: data file, visibility map file, and FSM file. Each index indicates a file if indexes are used. The following error message appears when you create a table after the maximum number of files is reached: 
could not create file

In this case, you need to delete some tables or upgrade the specifications of your cluster.

Table 2. Other limits
Item Limit
Root privilege of databases PolarDB PostgreSQL does not support the superuser privilege. Instead, it supports the polar_superuser privilege as a subset of the superuser privilege.
dblink/fdw Not supported.

Apsara PolarDB compatible with Oracle

Node specification Memory occupied by the file system Maximum number of files
polar.mysql.x2.medium 450 MB 1,026,048
polar.mysql.x4.large 850 MB 2,050,048
polar.mysql.x4.xlarge
polar.mysql.x8.xlarge
polar.mysql.x8.2xlarge
polar.mysql.x8.4xlarge
polar.mysql.x8.12xlarge
Maximum number of files: includes user table files, database system table files (approximately 1,000), and log files. An Apsara PolarDB table (non-partition table) occupies three files: data file, visibility map file, and FSM file. Each index indicates a file if indexes are used. The following error message appears when you create a table after the maximum number of files is reached: 
could not create file

In this case, you need to delete some tables or upgrade the specifications of your cluster.

Table 3. Other limits
Item Limit
Root privilege of databases PolarDB PostgreSQL does not support the superuser privilege. Instead, it supports the polar_superuser privilege as a subset of the superuser privilege.
dblink/fdw Not supported.