Connection pool exhaustion with Snowflake, Metabase v0.56

MOSTAFA · September 1, 2025, 5:12pm

After upgrading to Metabase v0.56, we're experiencing severe connection pool exhaustion with Snowflake, resulting in 120,000+ unnecessary USE DATABASE commands per day. Investigation reveals this is caused by the C3P0 connection pool library upgrade to version 0.11.2 in pull request #10 of the metabase/connection-pool repository.

C3P0 0.11.2 introduced JDBC 4.3 session boundary management (beginRequest()/endRequest() calls) that conflicts with Snowflake JDBC driver behavior. Connections remain in "idle cleanup" state much longer than previous C3P0 versions, causing pool exhaustion during business hours.

Connection Pool Data:
"db-2-snowflake": {
"numConnections": 15, // Pool maxed out
"numIdleConnections": 11, // Stuck in session cleanup
"numBusyConnections": 4, // Actually running queries
"maxPoolSize": 15, // Default limit
"numThreadsAwaitingCheckoutDefaultUser": 0
}

dragonsahead · September 1, 2025, 5:26pm

metabase 56 still uses connection-pool 1.2

github.com/metabase/metabase

deps.edn

6d086c35e


      
          ;; TODO: replace back to normal artifact
          io.github.metabase/macaw                  {:mvn/version "0.2.27"}             ; Parse native SQL queries
          io.github.resilience4j/resilience4j-retry ^:antq/exclude                      ; 2.x do not support Java 8
                                                    {:mvn/version "1.7.1"}              ; Support for retrying operations
          io.prometheus/simpleclient_hotspot        {:mvn/version "0.16.0"}             ; prometheus jvm collector
          junegunn/grouper                          {:mvn/version "0.1.1"}              ; Batch processing helper
          kixi/stats                                {:mvn/version "0.5.7"               ; Various statistic measures implemented as transducers
                                                     :exclusions  [org.clojure/data.avl]}
          lambdaisland/uri                          {:mvn/version "1.19.155"}           ; Used by openai-clojure
          medley/medley                             {:mvn/version "1.4.0"}              ; lightweight lib of useful functions
          metabase/connection-pool                  {:mvn/version "1.2.0"}              ; simple wrapper around C3P0. JDBC connection pools
          metabase/saml20-clj                       {:mvn/version "4.2.1"
                                                     :exclusions [; EE SAML integration TODO: bump version when we release the library
                                                                  org.bouncycastle/bcpkix-jdk15on
                                                                  org.bouncycastle/bcprov-jdk15on
                                                                  org.bouncycastle/bcpkix-jdk18on
                                                                  org.bouncycastle/bcprov-jdk18on]}
          metabase/throttle                         {:mvn/version "1.0.2"}              ; Tools for throttling access to API endpoints and other code pathways
          methodical/methodical                     {:mvn/version "1.0.127"}            ; drop-in replacements for Clojure multimethods and adds several advanced features
          metosin/malli                             {:mvn/version "0.19.1"}             ; Data-driven Schemas for Clojure/Script and babashka
          nano-id/nano-id                           {:mvn/version "1.1.0"}              ; NanoID generator for generating entity_ids

and just to be double sure, we’re using c3p0 10.x

github.com/metabase/metabase

deps.edn

6d086c35e


      
          com.github.pangloss/transducers           {:git/sha "c91d39046c8c64dc31b84ebb27154a8084fcda4c" ; like medley for transducers
                                                     :git/url "https://github.com/pangloss/transducers"}
          com.github.seancorfield/honeysql          {:mvn/version "2.7.1310"}           ; Honey SQL 2. SQL generation from Clojure data maps
          com.github.seancorfield/next.jdbc         {:mvn/version "1.3.1002"}            ; Talk to JDBC DBs
          com.github.steffan-westcott/clj-otel-api  {:mvn/version "0.2.8"}              ; Telemetry library
          com.github.vertical-blank/sql-formatter   {:mvn/version "2.0.5"}              ; Java SQL formatting library https://github.com/vertical-blank/sql-formatter
          com.google.guava/guava                    {:mvn/version "33.4.8-jre"}         ; dep for BigQuery, Spark, and GA. Require here rather than letting different dep versions stomp on each other — see comments on #9697
          com.h2database/h2                         ^:antq/exclude                      ; https://metaboat.slack.com/archives/CKZEMT1MJ/p1727191010259979
                                                    {:mvn/version "2.1.214"}            ; embedded SQL database
          com.ibm.icu/icu4j                         {:mvn/version "77.1"}               ; Used to transliterate Unicode characters into Latin characters
          com.mchange/c3p0                          {:mvn/version "0.10.1"}             ; DB connection pool
          com.snowplowanalytics/snowplow-java-tracker ^:antq/exclude                    ; 2+ depend on apache httpclient 5.x, but saml and clj-http depend on 4.x
                                                    {:mvn/version "1.0.1"}              ; Snowplow analytics
          com.sun.mail/jakarta.mail                 ^:antq/exclude                      ; 2+ changes imports from javax.mail to jakarta.mail
                                                    {:mvn/version "1.6.8"}              ; SMTP lib, required by postal
          com.taoensso/nippy                        {:mvn/version "3.6.0"}              ; Fast serialization (i.e., GZIP) library for Clojure
          com.vladsch.flexmark/flexmark             {:mvn/version "0.64.8"}             ; Markdown parsing
          com.vladsch.flexmark/flexmark-ext-autolink
          {:mvn/version "0.64.8"}             ; Flexmark extension for auto-linking bare URLs
          commons-codec/commons-codec               {:mvn/version "1.19.0"}             ; Apache Commons -- useful codec util fns
          commons-io/commons-io                     {:mvn/version "2.20.0"}             ; Apache Commons -- useful IO util fns

dragonsahead · September 1, 2025, 5:29pm

unless you’re forking the code and using an unreleased version of our pooler library

MOSTAFA · September 1, 2025, 5:48pm

@dragonsahead Thank you so much for checking the actual dependencies! I’m using the official release, but I mistakenly thought it was upgraded. I’m not sure why we're experiencing this spike after the new Metabase release, but I will continue to investigate.

dragonsahead · September 1, 2025, 5:49pm

please tell us which version you upgraded from so we can trace down what changed