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Introduce least-outstanding-connections load balancing (#282)

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Least outstanding connections load balancing can improve the load distribution between instances but for Pgcat it may also improve handling slow replicas that don't go completely down. With LoC, traffic will quickly move away from the slow replica without waiting for the replica to be banned.

If all replicas slow down equally (due to a bad query that is hitting all replicas), the algorithm will degenerate to Random Load Balancing (which is what we had in Pgcat until today).

This may also allow Pgcat to accommodate pools with differently-sized replicas.
This commit is contained in:
Mostafa Abdelraouf
2023-01-17 06:52:18 -06:00
committed by GitHub
parent ab0bad6da0
commit 7894bba59b
5 changed files with 177 additions and 7 deletions
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9
tests/ruby/helpers/pgcat_helper.rb
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@@ -5,7 +5,7 @@ require_relative 'pg_instance'
module Helpers
module Pgcat
def self.three_shard_setup(pool_name, pool_size, pool_mode="transaction")
def self.three_shard_setup(pool_name, pool_size, pool_mode="transaction", lb_mode="random")
user = {
"password" => "sharding_user",
"pool_size" => pool_size,
@@ -23,6 +23,7 @@ module Helpers
"#{pool_name}" => {
"default_role" => "any",
"pool_mode" => pool_mode,
"load_balancing_mode" => lb_mode,
"primary_reads_enabled" => false,
"query_parser_enabled" => false,
"sharding_function" => "pg_bigint_hash",
@@ -46,7 +47,7 @@ module Helpers
end
end
def self.single_instance_setup(pool_name, pool_size, pool_mode="transaction")
def self.single_instance_setup(pool_name, pool_size, pool_mode="transaction", lb_mode="random")
user = {
"password" => "sharding_user",
"pool_size" => pool_size,
@@ -64,6 +65,7 @@ module Helpers
"#{pool_name}" => {
"default_role" => "primary",
"pool_mode" => pool_mode,
"load_balancing_mode" => lb_mode,
"primary_reads_enabled" => false,
"query_parser_enabled" => false,
"sharding_function" => "pg_bigint_hash",
@@ -90,7 +92,7 @@ module Helpers
end
end
def self.single_shard_setup(pool_name, pool_size, pool_mode="transaction")
def self.single_shard_setup(pool_name, pool_size, pool_mode="transaction", lb_mode="random")
user = {
"password" => "sharding_user",
"pool_size" => pool_size,
@@ -111,6 +113,7 @@ module Helpers
"#{pool_name}" => {
"default_role" => "any",
"pool_mode" => pool_mode,
"load_balancing_mode" => lb_mode,
"primary_reads_enabled" => false,
"query_parser_enabled" => false,
"sharding_function" => "pg_bigint_hash",