How to Scale Postgres - Automation, Tuning & Sharding

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@LukasFittl How to Scale Postgres: Automation, Tuning & Sharding

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@LukasFittl

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Scaling Postgres

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Scaling Postgres

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Automation Handling 100s of database servers

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Consistency is key

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Infrastructure as Code

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Postgres Infrastructure as Code

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Demo: Managing Configuration using Terraform

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Cloud PaaS Synchronized Conﬁguration Terraform

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Cloud PaaS Synchronized Conﬁguration Terraform Access Control (Roles, pg_hba.conf) Terraform

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Cloud PaaS Synchronized Conﬁguration Terraform Parameter Groups Access Control (Roles, pg_hba.conf) Roles: Terraform HBA: Built-in Automatic Failover (for HA & Planned Updates) Built-in

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Cloud PaaS Synchronized Conﬁguration Terraform Parameter Groups Access Control (Roles, pg_hba.conf) Roles: Terraform HBA: Built-in Automatic Failover (for HA & Planned Updates) Built-in Read Replicas Built-in

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Cloud PaaS Self-Managed VM Synchronized Conﬁguration Terraform Parameter Groups ? Access Control (Roles, pg_hba.conf) Roles: Terraform HBA: Built-in ? Automatic Failover (for HA & Planned Updates) Built-in ? Read Replicas Built-in ? Backups Built-in ? Connection Pooling Manual Setup ?

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Cloud PaaS Self-Managed VM Synchronized Conﬁguration Terraform Parameter Groups ? Access Control (Roles, pg_hba.conf) Roles: Terraform HBA: Built-in ? Automatic Failover (for HA & Planned Updates) Built-in pg_auto_failover Read Replicas Built-in ? Backups Built-in ? Connection Pooling Manual Setup ?

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pg_auto_failover: Simple, automated failover

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pg_auto_failover

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Demo: Postgres HA using pg_auto_failover

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Tuning Making The Most Of Your Database Server

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work_mem tuning

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Out Of Memory vs Operations Spill To Disk

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Temporary Files Written pg_stat_statements.temp_blks_written pg_stat_database.temp_bytes

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Temporary Files Written (Per Query) log_temp_files = 0 Jan 20 09:18:58pm PST 28847 LOG: temporary file: path "base/pgsql_ pgsql_tmp28847.9", size 50658332 Jan 20 09:18:58pm PST 28847 STATEMENT: WITH servers AS ( SELECT …

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When Sorts Spill To Disk, Increase work_mem However, be aware of OOMs!

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When you get a lot of Out of Memory Errors Reduce work_mem!

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VACUUM

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autovacuum => SELECT pid, query FROM pg_stat_activity WHERE query LIKE 'autovacuum: %'; 10469 | autovacuum: VACUUM ANALYZE public.schema_columns 12848 | autovacuum: VACUUM public.replication_follower_stats 28626 | autovacuum: VACUUM public.schema_index_stats | (to prevent wraparound) (3 rows) pg_stat_activity

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autovacuum pg_stat_progress_vacuum relid: OID of the table phase: current VACUUM phase heap_blks_total: Heap Blocks Total heap_blks_scanned: Heap Blocks Scanned heap_blks_vacuumed: Heap Blocks Vacuumed …

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Reduce autovacuum_vacuum_cost_delay To Increase VACUUM Speed 80 MB/s 8 MB/s (20ms) (2ms) PG 12+ Older PG Default OS / Disk Reads

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Use Table Partitioning For Append-Only + Delete Workloads (e.g. Timeseries)

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Checkpoints

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Data Directory WAL WAL WAL Buffer Cache Checkpointer WAL Checkpoints Are Important For I/O Tuning

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16688 LOG: checkpoint starting: xlog xlog = WAL exceeded max_wal_size, checkpoint has to happen quickly time = checkpoint_timeout reached, checkpoint impact spread over time

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Checkpoint Statistics pg_stat_bgwriter checkpoints_timed: # of scheduled checkpoints checkpoints_req: # of requested checkpoints 1. Time Between Checkpoints 2. % of Timed Checkpoints

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Increase max_wal_size / Reduce checkpoint_timeout To Have More Timed Checkpoints (but be careful with recovery times)

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Tune checkpoint_completion_target To Control I/O Impact of Timed Checkpoints (Often 0.9 is a good value, but depends on I/O Subsystem & Workload)

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Demo: Postgres 13 WAL Monitoring

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Sharding Scaling Beyond The Limits of a Single Server

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Citus: Extension for Sharding Postgres

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Select from table Coordinator Table metadata Select from table_1001 Select from table_1003 Select from table_1002 Select from table_1004 Data node N Data node 2 Data node 1 Table_1001 Table_1003 Table_1002 Table_1004 Each node PostgreSQL with Citus installed 1 shard = 1 PostgreSQL table Sharding data across multiple nodes