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84th chunk of `doc/src/sgml/monitoring.sgml`
2a5f36ad0a71a85f7a3f18da4892e9df6fd9317dd56db1450000000100000fa2
 <symbol>INVALID_PROC_NUMBER</symbol> (-1) for a shared buffer.
      arg6 is true if the buffer was found in the pool, false if not.</entry>
    </row>
    <row>
     <entry><literal>buffer-flush-start</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid)</literal></entry>
     <entry>Probe that fires before issuing any write request for a shared
      buffer.
      arg0 and arg1 contain the fork and block numbers of the page.
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.</entry>
    </row>
    <row>
     <entry><literal>buffer-flush-done</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid)</literal></entry>
     <entry>Probe that fires when a write request is complete.  (Note
      that this just reflects the time to pass the data to the kernel;
      it's typically not actually been written to disk yet.)
      The arguments are the same as for <literal>buffer-flush-start</literal>.</entry>
    </row>
    <row>
     <entry><literal>wal-buffer-write-dirty-start</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when a server process begins to write a
      dirty WAL buffer because no more WAL buffer space is available.
      (If this happens often, it implies that
      <xref linkend="guc-wal-buffers"/> is too small.)</entry>
    </row>
    <row>
     <entry><literal>wal-buffer-write-dirty-done</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when a dirty WAL buffer write is complete.</entry>
    </row>
    <row>
     <entry><literal>wal-insert</literal></entry>
     <entry><literal>(unsigned char, unsigned char)</literal></entry>
     <entry>Probe that fires when a WAL record is inserted.
      arg0 is the resource manager (rmid) for the record.
      arg1 contains the info flags.</entry>
    </row>
    <row>
     <entry><literal>wal-switch</literal></entry>
     <entry><literal>()</literal></entry>
     <entry>Probe that fires when a WAL segment switch is requested.</entry>
    </row>
    <row>
     <entry><literal>smgr-md-read-start</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid, int)</literal></entry>
     <entry>Probe that fires when beginning to read a block from a relation.
      arg0 and arg1 contain the fork and block numbers of the page.
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.
      arg5 is the ID of the backend which created the temporary relation for a
      local buffer, or <symbol>INVALID_PROC_NUMBER</symbol> (-1) for a shared buffer.</entry>
    </row>
    <row>
     <entry><literal>smgr-md-read-done</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid, int, int, int)</literal></entry>
     <entry>Probe that fires when a block read is complete.
      arg0 and arg1 contain the fork and block numbers of the page.
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.
      arg5 is the ID of the backend which created the temporary relation for a
      local buffer, or <symbol>INVALID_PROC_NUMBER</symbol> (-1) for a shared buffer.
      arg6 is the number of bytes actually read, while arg7 is the number
      requested (if these are different it indicates a short read).</entry>
    </row>
    <row>
     <entry><literal>smgr-md-write-start</literal></entry>
     <entry><literal>(ForkNumber, BlockNumber, Oid, Oid, Oid, int)</literal></entry>
     <entry>Probe that fires when beginning to write a block to a relation.
      arg0 and arg1 contain the fork and block numbers of the page.
      arg2, arg3, and arg4 contain the tablespace, database, and relation OIDs
      identifying the relation.
      arg5 is the ID of the backend which created the temporary relation for a
      local buffer, or <symbol>INVALID_PROC_NUMBER</symbol> (-1) for a shared
Title: Built-in DTrace Probes in PostgreSQL (Buffer Flush, WAL, and SMGR)
Summary
This section describes DTrace probes in PostgreSQL related to buffer flushing, WAL (Write-Ahead Logging), and SMGR (Storage Manager). It covers probes that trigger before and after flushing a shared buffer. For WAL, it details probes that fire when a server process writes a dirty WAL buffer due to insufficient space and when a WAL buffer write is complete, including probes for WAL record insertion (specifying resource manager and info flags) and WAL segment switching. The SMGR probes indicate when reading or writing a block to a relation starts and completes, providing information about forks, block numbers, relation identifiers, the ID of the backend creating the temporary relation, and the number of bytes read or requested.