PG_WALSUMMARY(1)

📦 version 18.6, in opensuse-leap 16.0

✨ PG_WALSUMMARY ✨ (like, the manual page for pg_walsummary, section 1)

okay bestie, pull up a chair because we're about to talk about PostgreSQL 18.6 Documentation and the one tool that lets you peek inside WAL summary files 💅

🌸 NAME 🌸

pg_walsummary — print contents of WAL summary files

🎀 SYNOPSIS 🎀

pg_walsummary [option...] [file...]

🦋 DESCRIPTION 🦋

so pg_walsummary is the girl whose whole job is printing out the contents of WAL summary files. these are binary files that live in the pg_wal/summaries subdirectory of the data directory, and this tool converts them to text. no cap.

now, is this something you ordinarily need to do? bestie, no. WAL summary files primarily exist to support incremental backup. but for debugging purposes? it's giving useful. it's giving forensic. 🔥

here's the tea on how a WAL summary file is structured: it's indexed by tablespace OID, relation OID, and relation fork. for each relation fork, it stores the list of blocks that were modified by WAL within the range summarized in the file. iconic.

it can also store a "limit block," and the way that works is:

  • it's 0 if the relation fork was created or truncated within the relevant WAL range, otherwise
  • it's the shortest length to which the relation fork was truncated.

and if the relation fork was not created, deleted, or truncated within the relevant WAL range? then the limit block is undefined or infinite and will not be printed by this tool. so if you don't see it, that's why. mystery solved, you're welcome 🫶

💖 OPTIONS 💖

  • -i, --individual — okay so by default, pg_walsummary prints one line of output for each range of one or more consecutive modified blocks. this makes the output a whole lot briefer, because a relation where all blocks from 0 through 999 were modified will produce only one line of output rather than 1000 separate lines. this option says "no thanks, give me the long version" and requests a separate line of output for every modified block. 🌈
  • -q, --quiet — do not print any output, except for errors. lowkey the move when you just want to know whether a WAL summary file can be successfully parsed but you genuinely do not care about the contents. silence is golden ✨
  • -V, --version — display version information, then exit. that's it, that's the whole thing 👑
  • -?, --help — shows help about pg_walsummary command line arguments, and exits. bestie behavior fr fr 💅

🧚 ENVIRONMENT 🧚

the environment variable PG_COLOR specifies whether to use color in diagnostic messages. possible values are always, auto and never. (yes, auto is there, we love a middle ground 🍓)

⭐ SEE ALSO ⭐

⚠️ reminder that WAL summary files are binary and this tool is mostly for debugging — you're not normally supposed to be reading these by hand, but here you are, main character energy 🌸

and that's the whole page!! this was PostgreSQL 18.6, dated 2026, and honestly? she ate. periodt 💖🎀🦋

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