This technical presentation by EDB Dave Thomas, Systems Engineer provides an overview of: 1) BGWriter/Writer Process 2) Wall Writer Process 3) Stats Collector Process 4) Autovacuum Launch Process 5) Syslogger Process/Logger process 6) Archiver Process 7) WAL Send/Receive Processes

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Overview of Postgres Utilities Processes
Dave Thomas | 8.22.13
Techie Topic Series

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• Overview – What are all these processes?
• Logger Process
• Checkpointer Process
• Writer Process
• WAL Writer Process
• Autovacuum Launcher Process
• Stats Collector Process
• Streaming Replication Process
• Resources
Presentation Agenda

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What are all these processes?
• PostgreSQL utilizes separate processes instead of threads,
which results in the above ps output for a freshly started
cluster
• Each connection to the cluster will cause the postmaster to
spawn a process which may look like the following:
• The above shows a connection from 127.0.0.1 to the test
database by the user Postgres.

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• Logging is an optional process, the default is OFF
• All the utility processes + user backends + postmaster daemon attach to
the logger process
• All process information is logged under $PGDATA/pg_log in the file name
specified by log_filename
− If the data directory is created with INITDB command, then the pg_log
directory will need to be created manually.
− You can also log to syslog and CSV formatted files
• Increasing the amount of logging will increase the I/O load on the server.
• http://www.enterprisedb.com/docs/en/9.2/pg/runtime-config-logging.html
Logger Process

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• This process is responsible for flushing all dirty data pages to disk (called
a checkpoint)
− This process can cause a significant I/O load on the server.
• Checkpoints are performed every checkpoint_timeout seconds or when
all checkpoint_segments are filled, whichever comes first.
• More frequent checkpoints will provide for faster after-crash recovery, but
this must be balanced by the increased I/O load generated.
• http://www.enterprisedb.com/docs/en/9.2/pg/wal-configuration.html
Checkpointer Process

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• Also known as BGWRITER process and is a mandatory process.
• Wakes every bgwriter_delay seconds and searches through the shared buffer
pool looking for modified pages, writes them to disk, and evicts those pages
from the shared buffer pool.
• No more than bgwriter_lru_maxpages buffers will be written by the
background writer in a given pass.
• http://www.enterprisedb.com/docs/en/9.2/pg/runtime-config-
resource.html#RUNTIME-CONFIG-RESOURCE-BACKGROUND-WRITER
Writer Process

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• This is a mandatory process
• Writes and syncs Write Ahead Logs(WAL) to disk upon transaction
commit
• WALs allow transactions to be recovered in the event of a system
crash
• http://www.enterprisedb.com/docs/en/9.2/pg/wal-configuration.html
WAL Writer Process

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• Autovacuuming is an optional process, default is ON.
• Automates the execution of VACUUM and ANALYZE commands
• A daemon which spawns autovacuum worker processes for each
database
− Starts one worker on each database (up to autovacuum_max_workers)
every autovacuum_naptime seconds
− Worker processes check each table and index in a database and
executes VACUUM or ANALYZE as needed.
• http://www.enterprisedb.com/docs/en/9.2/pg/runtime-config-autovacuum.html
Autovacuum Launcher Process

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• Stats collector process is an optional process, default is ON.
• Collects information about cluster activity.
− Number of access to the tables and indexes
− Total number of rows in each table
− Information about VACUUM and ANALYZE actions for each table.
• Collection of statistics adds some overhead to query execution, but allows
the query planner to make better choices.
• http://www.enterprisedb.com/docs/en/9.2/pg/monitoring-stats.html
Stats Collector Process

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• WAL Sender
− This process sends WALs the standby server.
− One process for each standby server.
• WAL Receiver
− This process receives WALs from the the primary server.
− The WALs are then replayed to bring the standby in sync with the primary.
• http://www.enterprisedb.com/docs/en/9.2/pg/warm-standby.html#STREAMING-REPLICATION
Streaming Replication Processes

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• Software Downloads & Documentation
− EnterpriseDB > Products > Postgres Plus Advanced Server
− EnterpriseDB > Products > Postgres Enterprise Manager
− EnterpriseDB > Products > Documentation
− EnterpriseDB > Products > Subscriptions
• Tutorials, Quick Starts, Webcasts, White Papers &
Community
− EnterpriseDB > Resources
• Email us!
− Dave.thomas@enterprisedb.com
− lyn.vercellone@enterprisedb.com
− sales@enterprisedb.com
Additional Resources- on EnterpriseDB.com

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