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1. IL-0313 Decagon voice requests stalled for exactly 300 seconds behind self-managed PgBouncer and exhausted the SQLAlchemy pool

   Decagon2026

   Symptoms

   During the first production canary of Decagon's move from GCP's managed connection pooler to self-managed PgBouncer, a small number of voice requests stalled mid-conversation and timed out after exactly 300 seconds. Other requests failed much earlier because the SQLAlchemy connection pool was exhausted.

   Intermittent timeoutsConnection pool exhaustion

   Trigger

   The move from GCP's managed connection pooler to self-managed PgBouncer enabled a different TLS path between PgBouncer and Postgres, which supplied the last of three conditions needed to expose the bug.

   Root cause

   Software defect

   Component

   DatabaseDatabase proxy and connection pooler

   Contributing factor

   Unrepresentative stagingUnverified assumption

   Detection

   Sentry errors ("SSL connection has been closed unexpectedly") and SQLAlchemy connection-pool timeouts during the production canary, followed by a comparison of application spans with Postgres query timings.

   Remediation

   • Shortened the application name parameter so the ParameterStatus packet stayed below PgBouncer's small-packet parsing threshold

   Action items

   • Fix PgBouncer upstream so it checks SSL_pending() before going back to wait on epoll()

   Lessons

   Decagon's lesson is that an infrastructure migration does not only change one's own systems but can also expose latent bugs elsewhere in the stack: the move to self-managed PgBouncer supplied the last condition for a long-standing edge case involving SQLAlchemy, PgBouncer, OpenSSL and the PostgreSQL wire protocol.

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