fix(spanner): update dynamic channel pool default configuration#13646
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Set Spanner DCP defaults to maxRpcPerChannel=25, minRpcPerChannel=15, scaleDownInterval=3m, initSize=4, maxChannels=10, minChannels=2.
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This pull request updates several default configuration values for the Dynamic Channel Pool (DCP) in SpannerOptions.java. Specifically, it decreases the default maximum concurrent RPCs per channel from 90 to 25, increases the default initial size from 1 to 4, decreases the default maximum channels from 256 to 10, and increases the default minimum channels from 1 to 2. There are no review comments, and I have no feedback to provide.
olavloite
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The change and values LGTM, but can we add tests that verify that our defaults are really used, primarily to prevent accidental regressions in the future?
| // Dynamic Channel Pool (DCP) default values and bounds | ||
| /** Default max concurrent RPCs per channel before triggering scale up. */ | ||
| public static final int DEFAULT_DYNAMIC_POOL_MAX_RPC = 90; | ||
| public static final int DEFAULT_DYNAMIC_POOL_MAX_RPC = 25; |
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I'm a bit surprised that we can make this change without the need to change any tests. That means that we have no tests that verify our defaults. Can we add that?
I understand that those tests aren't doing much in most cases, but having tests that verify default values is a good protection against accidental regressions in the future (e.g. if someone accidentally overrides a method that returns the default value, and thereby unintentionally returns a different default etc.)
Add explicit literal assertions for the DCP default constants so any change to the defaults fails a unit test and must be made deliberately.
🤖 I have created a release *beep* *boop* --- <details><summary>1.88.0</summary> ## [1.88.0](v1.87.1...v1.88.0) (2026-07-06) ### Features * **auth:** Add support for Regional Access Boundaries ([#13499](#13499)) ([b721e43](b721e43)) * automate libraries-bom tag and release creation on release publish ([#13655](#13655)) ([7a7e2ff](7a7e2ff)) * **bigquery-jdbc:** add `EnableProjectDiscovery` connection property for metadata methods ([#13344](#13344)) ([ab9669a](ab9669a)) * **bigquery-jdbc:** migrate statement execution thread tracking to connection-scoped executor ([#13454](#13454)) ([341e51a](341e51a)) * **bigquery-jdbc:** respect standard JVM trustStore properties by default ([#13435](#13435)) ([7af3224](7af3224)) * **bigquery-jdbc:** support connection-scoped executor isolation and dynamic queue warnings ([#13413](#13413)) ([79e26b8](79e26b8)) * **bigquery:** add internal listProjects API to core client ([#13429](#13429)) ([3580407](3580407)) * **bigtable:** route point read rows to shim ([#13542](#13542)) ([2c7e5f5](2c7e5f5)) * **deps:** add jspecify to shared dependencies ([#13412](#13412)) ([582053d](582053d)) * enable self-signed JWTs by default in ServiceOptions ([#13338](#13338)) ([110d2b7](110d2b7)) * **gapic-generator:** Add NullMarked annotation to generated classes ([#13517](#13517)) ([825dadd](825dadd)) * **google/cloud/agentregistry/v1:** onboard a new library ([#13509](#13509)) ([6728816](6728816)) * scale up connection worker pool based on latency ([#13384](#13384)) ([eb379b3](eb379b3)) * **spanner:** add settings for gRCP keep-alive ([#13643](#13643)) ([9d78307](9d78307)) * **spanner:** auth login support for Spanner Omni endpoints ([#13470](#13470)) ([55930b4](55930b4)) * **storage:** add checksum validation in the json read channel ([#13270](#13270)) ([872d7b7](872d7b7)) * **storage:** add checksum validation on json read paths ([#13269](#13269)) ([396b042](396b042)) * **storage:** add full object checksum validation for bidi flow ([#13266](#13266)) ([9113d80](9113d80)) * **storage:** add full object checksum validation for grpc flow ([#13265](#13265)) ([a5ba606](a5ba606)) * **storage:** Adding CumulativeHasher wrapper class for Full object … ([#13239](#13239)) ([bd40324](bd40324)) * **storage:** adding disabling option for bidi reads ([#13506](#13506)) ([591cae0](591cae0)) * **storage:** log additional bytes received from GCS in read path ([#13427](#13427)) ([9492aa2](9492aa2)) * **storage:** update compose sample to support deleteSourceObjects option ([#13493](#13493)) ([50a8658](50a8658)) * use self-signed JWTs in Spanner MutableCredentials ([#13381](#13381)) ([29543a2](29543a2)) ### Bug Fixes * Add logging-logback to gapic-libraries-bom ([#13663](#13663)) ([512e370](512e370)) * **auth:** Fix UserCredentials serialization clientSecret leak ([#13465](#13465)) ([2d9d01c](2d9d01c)) * **auth:** handle missing APPDATA on Windows gracefully ([#13471](#13471)) ([77e84a9](77e84a9)), closes [#12565](#12565) * **bigquery-jdbc:** add proper version to BigQueryDriver ([#13294](#13294)) ([9fd84fc](9fd84fc)) * **bigquery-jdbc:** avoid rollback on statement close in manual commit mode ([#13503](#13503)) ([79bbee1](79bbee1)) * **bigquery-jdbc:** correct `FilterTablesOnDefaultDataset` fallback logic ([#13625](#13625)) ([f7eb23d](f7eb23d)) * **bigquery-jdbc:** ensure largeResults are handled in PreparedStatement ([#13496](#13496)) ([d3e7a19](d3e7a19)) * **bigquery-jdbc:** ensure test uses unique dataset & cleans up ([#13587](#13587)) ([a6bb362](a6bb362)) * **bigquery-jdbc:** explicitly set location when available for temporary dataset ([#13508](#13508)) ([40cd0a7](40cd0a7)) * **bigquery-jdbc:** propagate connection proxy settings to auth library ([#13539](#13539)) ([87dda5d](87dda5d)) * **bigquery-jdbc:** shade org.slf4j ([#13547](#13547)) ([7ef1312](7ef1312)) * **bigquery-jdbc:** update format validation tests to create tables for the test ([#13588](#13588)) ([4bb3a61](4bb3a61)) * **bigquery-jdbc:** update Maven Central artifact link in the README ([#13563](#13563)) ([8707a65](8707a65)) * **bigquery:** retry cancel job and routine creation on transient HTTP 5xx errors ([#13416](#13416)) ([35eb041](35eb041)) * **bigquery:** route JOB_CREATION_REQUIRED through fast query path ([#13437](#13437)) ([64cde7f](64cde7f)) * **bigquery:** Update fast query path to allow jobTimeoutMs in the request ([#13502](#13502)) ([1a6f4d5](1a6f4d5)) * **bigtable:** honour session_load override when server-returned session_load is 0 ([#13629](#13629)) ([b56f9b8](b56f9b8)) * **bqjdbc:** pass rowsInPage with TableResult ([#13238](#13238)) ([203a91e](203a91e)) * **ci:** build dependencies before convergence check ([#13638](#13638)) ([9de3209](9de3209)) * **ci:** ignore SNAPSHOT suffix in flatten-plugin check ([#13639](#13639)) ([bb65627](bb65627)) * **ci:** run root install in dependency convergence check ([#13666](#13666)) ([86d35e4](86d35e4)) * **ci:** skip existing-versions-check for gapic-generator-java-root ([#13590](#13590)) ([a1f3b8a](a1f3b8a)) * **datastore:** Configure TraceExporter with Datastore credentials in E2E tests ([#13627](#13627)) ([d281a62](d281a62)) * **datastore:** disable built-in OpenTelemetry SDK when metrics export is disabled ([#13543](#13543)) ([53b7142](53b7142)) * **datastore:** reduce flakiness of E2E tracing tests ([#13645](#13645)) ([8afc0ab](8afc0ab)) * **deps:** update dependency com.google.apis:google-api-services-bigquery to v2-rev20260612-2.0.0 ([#13570](#13570)) ([ca5ff79](ca5ff79)) * **deps:** update dependency com.google.apis:google-api-services-dns to v1-rev20260616-2.0.0 ([#12796](#12796)) ([0dd60ca](0dd60ca)) * **deps:** update dependency com.google.cloud:google-cloud-pubsub-bom to v1.151.0 ([#12097](#12097)) ([d169006](d169006)) * **deps:** update dependency com.google.cloud:libraries-bom to v26.84.0 ([#12663](#12663)) ([95c7774](95c7774)) * **deps:** update first-party storage dependencies to v1-rev20260524-2.0.0 ([#13406](#13406)) ([bdeedb8](bdeedb8)) * exclude java-vertexai from existing versions check ([#13632](#13632)) ([edaa4e3](edaa4e3)) * fallback on VPC ([#13567](#13567)) ([e8c428d](e8c428d)) * **java-cloud-bom:** execute pre-install pass in GHA release notes generator ([#13608](#13608)) ([c365c10](c365c10)) * **release:** check remote tags using git ls-remote to prevent already exists error ([#13574](#13574)) ([6cf0567](6cf0567)) * **spanner:** fail fast when inline-begin DML returns no transaction id ([#13536](#13536)) ([94315ce](94315ce)) * **spanner:** pin inline read-write transactions to default endpoint ([#13562](#13562)) ([6908dee](6908dee)) * **spanner:** remove explicit tink version to resolve dependency convergence conflict ([#13602](#13602)) ([863c26e](863c26e)) * **spanner:** update dynamic channel pool default configuration ([#13646](#13646)) ([37b77c3](37b77c3)) ### Dependencies * Add org.bouncycastle:bcprov-jdk18on to java-shared-dependencies ([#13531](#13531)) ([e3d2082](e3d2082)) * **auth:** Update commons-codec to v1.18.0 ([#13598](#13598)) ([fd89957](fd89957)) * Update gapic-showcase to v0.41.0 ([#13582](#13582)) ([09faaac](09faaac)) * Upgrade google-http-client to v2.1.1 ([#13578](#13578)) ([6abef19](6abef19)) ### Documentation * add instructions for manual code generation checks in CI ([#13596](#13596)) ([f6162e2](f6162e2)) </details> --- This PR was generated with [Release Please](https://github.com/googleapis/release-please). See [documentation](https://github.com/googleapis/release-please#release-please). --------- Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>
Set Spanner DCP defaults to maxRpcPerChannel=25, minRpcPerChannel=15, scaleDownInterval=3m, initSize=4, maxChannels=10, minChannels=2.
Internal Ref: go/dynamic-channel-pooling-non-sab