{"Entry":{"collection":"guc","key":"wal_block_size","name":"wal_block_size","aliases":[],"metadata":{"baseline":false,"boot_human":"Not specified","boot_val":null,"category":"Preset Options","category_zh":"","changed_in":[],"changes":[{"documentation_changed":false,"fields":{},"from":"8.3","status":"added","to":"8.4"}],"content_hash":"06963e5195da0fae43a2e28c0aa99a76ed1d7ccc9019b45004213f1ebd2a72da","context":"","default_changed_in":[],"default_history":[{"from":"9.0","to":"19","value":"8192"}],"editorial":{"advice":{"olap":"Not tunable. Use wal_block_size to verify format, build, or resource assumptions on analytical nodes and keep every read/write candidate compatible.","oltp":"Not tunable. Record wal_block_size as a deployment/capability fact; if it is unexpected, fix the binary, initdb, or database-creation process rather than trying SET.","small":"Not tunable. Preserve it in inventory and incident reports; do not custom-build or rebuild merely to change it without a demonstrated compatibility need."},"mechanism":["Shows the block size in the write ahead log. It is read-only and cannot be changed with SET or configuration-file edits.","It reflects XLOG_BLCKSZ, normally 8 KiB, chosen at build time and used for WAL I/O buffers.","Interpret it with block_size, wal_segment_size, segment_size. Applications and operations tooling may read wal_block_size for capability or environment detection, but cannot SET it; cross-cluster comparisons must account for build, initdb, and current-database differences."],"pitfalls":["Trying to change read-only wal_block_size with SET or a configuration file.","Assuming every cluster, database, or vendor build reports the same value.","Ignoring the value in file-format or feature-compatibility checks.","Treating reported metadata as a performance target instead of an environment fact."],"references":[{"title":"PostgreSQL 19 Beta 4: wal_block_size","url":"https://www.postgresql.org/docs/19/runtime-config-preset.html#GUC-WAL-BLOCK-SIZE"},{"title":"PostgreSQL 19 release notes","url":"https://www.postgresql.org/docs/19/release-19.html"}],"related":["block_size","wal_segment_size","segment_size","data_checksums","server_version_num","data_directory_mode"],"summary":"wal_block_size — Shows the block size in the write ahead log. Observed in PG9.0–19 Beta 4; its last measured boot default is 8192 in PG19 Beta 4, with internal context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA."},"enumvals":[],"first_version":"8.4","group":"Preset Options","group_slug":"preset","imported_at":"2026-09-27T17:57:32.313722+08:00","intro_commit":{},"key":"wal_block_size","last_version":"20","max_val":"","min_val":"","name":"wal_block_size","position":462,"present_in":["8.4","9.0","9.1","9.2","9.3","9.4","9.5","9.6","10","11","12","13","14","15","16","17","18","19","20"],"short_desc":"Reports the size of a WAL disk block.","short_desc_zh":"","source_rev":"english-manuals:83e9c5ac3564705e7caeaaee4d6e3a8f995a1b0c2e38a685eb5e3355fbcff8dc","unit":"","vartype":"integer"}},"Definition":{"Collection":"guc","Key":"wal_block_size","SourceDatabase":"center","Version":"18","SourceTable":"guc","SourceKey":"wal_block_size","SourceRevision":"english-manuals:83e9c5ac3564705e7caeaaee4d6e3a8f995a1b0c2e38a685eb5e3355fbcff8dc","Facts":{"boot_val":"8192","category":"Preset Options","context":"internal","description":"Reports the size of a WAL disk block. It is determined by the value of XLOG_BLCKSZ when building the server. The default value is 8192 bytes.","doc":{"anchor":"GUC-WAL-BLOCK-SIZE","file":"runtime-config-preset.html","lang":"en","sha256":"4dbfec727b9cee838adefb8a766217748d91ab90190b452a58cec737459582ce","slug":"18"},"documented":true,"enumvals":null,"extra_desc":null,"lang":"en","max_val":"8192","metadata_version":"18","min_val":"8192","name":"wal_block_size","short_desc":"Shows the block size in the write ahead log.","source":"pg-settings-source-snapshot","unit":null,"vartype":"integer"},"ManualEvidence":{"doc":{"anchor":"GUC-WAL-BLOCK-SIZE","file":"runtime-config-preset.html","lang":"en","sha256":"4dbfec727b9cee838adefb8a766217748d91ab90190b452a58cec737459582ce","slug":"18"}},"MeasuredEvidence":{"metadata_version":"18"}},"Text":{"Collection":"guc","Key":"wal_block_size","SourceDatabase":"center","Version":"18","Locale":"en","Title":"wal_block_size","Summary":"Reports the size of a WAL disk block. It is determined by the value of XLOG_BLCKSZ when building the server. The default value is 8192 bytes.","BodyHTML":"\u003cp\u003eReports the size of a WAL disk block. It is determined by the value of XLOG_BLCKSZ when building the server. The default value is 8192 bytes.\u003c/p\u003e","SourceRevision":"english-manuals:83e9c5ac3564705e7caeaaee4d6e3a8f995a1b0c2e38a685eb5e3355fbcff8dc","ContentHash":"7e06d59849642c9a8a18a657b4ad6c0ddf3696f47a551f1ba7e4ed264f5a1183","Payload":{"description":"Reports the size of a WAL disk block. It is determined by the value of XLOG_BLCKSZ when building the server. The default value is 8192 bytes."}},"RequestedLocale":"zh-Hans","Fallback":true,"Versions":["10","11","12","13","14","15","16","17","18","19","20","8.4","9.0","9.1","9.2","9.3","9.4","9.5","9.6"],"Locales":["en"],"Signatures":null,"Spellings":null,"SQLState":null,"Evidence":null}