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CONFIG_IP_VS_TAB_BITS: IPVS connection table size (the Nth power of 2)

General informations

The Linux kernel configuration item CONFIG_IP_VS_TAB_BITS has multiple definitions:

IPVS connection table size (the Nth power of 2) found in net/ipv4/ipvs/Kconfig

The configuration item CONFIG_IP_VS_TAB_BITS:

Help text

The IPVS connection hash table uses the chaining scheme to handle hash collisions. Using a big IPVS connection hash table will greatly reduce conflicts when there are hundreds of thousands of connections in the hash table.

Note the table size must be power of 2. The table size will be the value of 2 to the your input number power. The number to choose is from 8 to 20, the default number is 12, which means the table size is 4096. Don't input the number too small, otherwise you will lose performance on it. You can adapt the table size yourself, according to your virtual server application. It is good to set the table size not far less than the number of connections per second multiplying average lasting time of connection in the table. For example, your virtual server gets 200 connections per second, the connection lasts for 200 seconds in average in the connection table, the table size should be not far less than 200x200, it is good to set the table size 32768 (2**15).

Another note that each connection occupies 128 bytes effectively and each hash entry uses 8 bytes, so you can estimate how much memory is needed for your box.

IPVS connection table size (the Nth power of 2) found in net/netfilter/ipvs/Kconfig

The configuration item CONFIG_IP_VS_TAB_BITS:

Help text

The IPVS connection hash table uses the chaining scheme to handle hash collisions. Using a big IPVS connection hash table will greatly reduce conflicts when there are hundreds of thousands of connections in the hash table.

Note the table size must be power of 2. The table size will be the value of 2 to the your input number power. The number to choose is from 8 to 20, the default number is 12, which means the table size is 4096. Don't input the number too small, otherwise you will lose performance on it. You can adapt the table size yourself, according to your virtual server application. It is good to set the table size not far less than the number of connections per second multiplying average lasting time of connection in the table. For example, your virtual server gets 200 connections per second, the connection lasts for 200 seconds in average in the connection table, the table size should be not far less than 200x200, it is good to set the table size 32768 (2**15).

Another note that each connection occupies 128 bytes effectively and each hash entry uses 8 bytes, so you can estimate how much memory is needed for your box.

You can overwrite this number setting conn_tab_bits module parameter or by appending ip_vs.conn_tab_bits=? to the kernel command line if IP VS was compiled built-in.

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