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A Clojure toolbox for inspecting and diagnosing PostgreSQL databases.

com.github.perrygeo/postgres-extras-clj {:mvn/version "0.1.17"}

🐘 Motivation

PostgreSQL is a fantastic database but using it in production requires some care, as do all databases. The postgres system catalogs allow us to monitor things like query performance, connection management, index efficiency, disk usage, and MVCC bloat. But accessing that information requires some arcane knowledge and reasonably hardcore SQL skills.

This project was inspired by the rustprooflabs pgdd extension and by the phoenix web framework which ships with a developer-centric, postgres-specific dashboard based on ecto_psql_extras. Both projects demonstrate that high-level database tooling can, and probably should, be built on top of the system catalogs. Understanding your database isn't optional.

postgres-extras-clj provides this missing toolkit for Clojure developers.

The SQL logic lives in resources/sql/*.sql and is formatted with pgFormat for consistency. SQL is annotated with HugSQL comments to turn them into clojure fns via macro magic. Instead of a web interface or postgres extension, postgres-extras-clj.core provides a clojure namespace with a few dozen useful functions that query system tables and return diagnostics as plain data structures. The goal is to run with limited, SELECT-only privileges of system schemas and tables (with a few noted exceptions).

All you need is a JDBC connection and a REPL.

📚 Data Dictionary

The data dictionary functionality is based on pgdd. These include COMMENTS and are helpful for understanding the structure of your database, from a data modeling lens.

columnsList all database column objects
databasesList all databases
functionsList all function objects in current database
indexesList all index objects in current database
schemasList all shemas in current database
partition-childrenList all child partitions in current database
partition-parentsList all parent partition tables in current database
tablesList all table objects in current database
viewsList all view objects in current database

To get a full map of data objects, use (read-data-dictionary db) which returns a map, with keywords mirroring the above functions.

🛠️ Operational Diagnostics

Diagnostic stats based on ecto_psql_extras. These are valuable for looking at your database through an operations or DBA lens.

all-locksQueries with active locks
bloatTable and index "bloat" in your database ordered by most wasteful
blockingQueries holding locks other queries are waiting to be released
cache-hitIndex and table hit rate
callsQueries that have the highest frequency of execution
connectionsReturns the list of all active database connections
db-settingsValues of selected PostgreSQL settings
duplicate-indexesMultiple indexes that have the same set of columns, same opclass, expression and predicate
extensionsAvailable and installed extensions
health-checkChecks the db for liveliness
index-cache-hitCalculates your cache hit rate for reading indexes
index-sizeThe size of indexes, descending by size
index-usageIndex hit rate (effective databases are at 99% and up)
kill-all!Kill all the active database connections
locksQueries with active exclusive locks
long-running-queriesAll queries longer than the threshold by descending duration
null-indexesFind indexes with a high ratio of NULL values
outliersQueries that have longest execution time in aggregate.
records-rankAll tables and the number of rows in each ordered by number of rows descending
seq-scansCount of sequential scans by table descending by order
table-cache-hitCalculates your cache hit rate for reading tables
table-indexes-sizeTotal size of all the indexes on each table, descending by size
table-sizeSize of the tables (excluding indexes), descending by size
total-index-sizeTotal size of all indexes in MB
total-table-sizeSize of the tables (including indexes), descending by size
unused-indexesUnused and almost unused indexes
vacuum-statsDead rows and whether an automatic vacuum is expected to be triggered

To get a full map of diagnostic stats, use (read-stats db) which returns a map, with keywords mirroring the above functions.

Use the (diagnose (read-stats db)) and (diagnose-warnings (read-stats db)) functions to evaluate the stats according to a set of heuristics.


Check out the examples if you're looking to create a fresh namespace.

The following is a REPL demonstration of postgres-extras-clj with the next.jdbc adapter. Run clj -M:dev then evaluate the following forms

(require '[postgres-extras-clj.core :as pgex] :reload-all)
(require '[hugsql.core :as hugsql])
(require '[ :as next-adapter])
(require '[next.jdbc :as jdbc])

(def db

(hugsql/set-adapter! (next-adapter/hugsql-adapter-next-jdbc))

For this example, wer'e using a next.jdbc datasource but there are other options, see the HugSQL Adapters documentation.

Do a quick health check

(pgex/health-check db)
; {:now #inst "2024-07-05T18:04:57.506678000-00:00",
;  :version "PostgreSQL 16.1 (Debian 16.1-1.pgdg110+1) on x86_64-pc-linux-gnu..."}

Generate a data dictionary summarizing all major objects in your database.

(def dd (pgex/read-data-dictionary db))
(keys dd)
; (:databases
;  :columns
;  :functions
;  :indexes
;  :schemas
;  :tables
;  :views 
;  :partition-children
;  :partition-parents)

(rand-nth (:tables dd))
; {:size_pretty "16 kB",
;  :description nil,
;  :owned_by "postgres",
;  :size_plus_indexes "48 kB",
;  :rows 1,
;  :oid 19789,
;  :data_type "table",
;  :size_plus_indexes_bytes 49152,
;  :s_name "public",
;  :system_object false,
;  :t_name "users",
;  :size_bytes 16384,
;  :bytes_per_row 16384}

Create a full map of diagnostic stats.

(def stats (pgex/read-stats db))
(keys stats)
; (:duplicate-indexes
;  :db-settings
;  :locks
;  :vacuum-stats
;  :index-usage
;  :total-index-size
;  :cache-hit
;  :health-check
;  :records-rank
;  :null-indexes
;  :index-cache-hit
;  :all-locks
;  :outliers
;  :long-running-queries
;  :extensions
;  :total-table-size
;  :unused-indexes
;  :bloat
;  :calls
;  :table-size
;  :connections
;  :table-cache-hit
;  :table-indexes-size
;  :blocking
;  :seq-scans
;  :index-size)

(rand-nth (:connections stats))
; {:username "postgres"
;  :client_address ""
;  :application_name "psql"}

All of the stats and data dictionary keywords mirror the name of a public function in the postgres-extras-clj.core namespace so you can invoke them selectively, instead of getting them from the full map.

(rand-nth (pgex/tables db))
; {:size_pretty "16 kB",
;  :description nil,
;  :owned_by "postgres",
;  :size_plus_indexes "48 kB",
;  :rows 1,
;  :oid 19789,
;  :data_type "table",
;  :size_plus_indexes_bytes 49152,
;  :s_name "public",
;  :system_object false,
;  :t_name "users",
;  :size_bytes 16384,
;  :bytes_per_row 16384}

(rand-nth (pgex/connections db))
; {:username "postgres"
;  :client_address ""
;  :application_name "psql"}

Read stats and print the default diagnostics:

;; warnings only
(doseq [w (pgex/diagnose-warnings (pgex/read-stats db))]
  (println (:message w)))

The default-diagnostic-fns can be overridden. To create your own diagnostics:

(def unrealistic-expectations
   {:pred #(> (:ratio %) 0.999)
    :onfalse "The cache hit ratio is not as insanely high as I'd like."
    :idfn :name}})

(doseq [w (pgex/diagnose-warnings
           (pgex/read-stats db)
           :diagnostic-fns unrealistic-expectations)]
  (println (:message w)))

; ! Warning :table-cache-hit, message_topics, The cache hit ratio is not as insanely high as I'd like.
; {:ratio 0.9806201550387597, :schema "public", :name "message_topics", :buffer_hits 253, :block_reads 5, :total_read 258}
; ... many more


Test runner with coverage

clj -X:test

Run NREPL and interactive terminal REPL in one

clj -M:dev

Build a jar. Output in ./target/com.github.perrygeo/postgres-extras-clj-*.jar

clj -T:build jar

Deploy to Clojars. Set CLOJARS_USERNAME and CLOJARS_PASSWORD env vars. Assumes that clj -T:build jar has already been run.

clj -T:build deploy


Copyright © 2024 Matthew T. Perry (perrygeo). Distributed under the MIT license.

The credit for the SQL query logic goes to the fantastic work done by these three projects:

Their licenses (all MIT) are included in the SQL files.

Can you improve this documentation? These fine people already did:
Matthew Perry & Matthew T. Perry
Edit on GitHub

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