diff options
Diffstat (limited to 'doc/src')
| -rw-r--r-- | doc/src/sgml/generic-wal.sgml | 32 |
1 files changed, 18 insertions, 14 deletions
diff --git a/doc/src/sgml/generic-wal.sgml b/doc/src/sgml/generic-wal.sgml index 2398d860037..147d456d34c 100644 --- a/doc/src/sgml/generic-wal.sgml +++ b/doc/src/sgml/generic-wal.sgml @@ -31,15 +31,18 @@ <listitem> <para> - <function>page = GenericXLogRegister(state, buffer, isNew)</> — - register a buffer to be modified within the current generic WAL + <function>page = GenericXLogRegisterBuffer(state, buffer, flags)</> + — register a buffer to be modified within the current generic WAL record. This function returns a pointer to a temporary copy of the buffer's page, where modifications should be made. (Do not modify the - buffer's contents directly.) The third argument indicates if the page - is new; if true, this will result in a full-page image rather than a - delta update being included in the WAL record. - <function>GenericXLogRegister</> can be repeated if the WAL-logged - action needs to modify multiple pages. + buffer's contents directly.) The third argument is a bitmask of flags + applicable to the operation. Currently the only such flag is + <literal>GENERIC_XLOG_FULL_IMAGE</>, which indicates that a full-page + image rather than a delta update should be included in the WAL record. + Typically this flag would be set if the page is new or has been + rewritten completely. + <function>GenericXLogRegisterBuffer</> can be repeated if the + WAL-logged action needs to modify multiple pages. </para> </listitem> @@ -71,13 +74,13 @@ <itemizedlist> <listitem> <para> - No direct modifications of buffers are allowed! All modifications - must be done in copies acquired from <function>GenericXLogRegister()</>. + No direct modifications of buffers are allowed! All modifications must + be done in copies acquired from <function>GenericXLogRegisterBuffer()</>. In other words, code that makes generic WAL records should never call <function>BufferGetPage()</> for itself. However, it remains the caller's responsibility to pin/unpin and lock/unlock the buffers at appropriate times. Exclusive lock must be held on each target buffer - from before <function>GenericXLogRegister()</> until after + from before <function>GenericXLogRegisterBuffer()</> until after <function>GenericXLogFinish()</>. </para> </listitem> @@ -145,10 +148,11 @@ <listitem> <para> - If a registered buffer is not new, the generic WAL record contains - a delta between the old and the new page images. This delta is based - on byte-by-byte comparison. This is not very compact for the case of - moving data within a page, and might be improved in the future. + If <literal>GENERIC_XLOG_FULL_IMAGE</> is not specified for a + registered buffer, the generic WAL record contains a delta between + the old and the new page images. This delta is based on byte-by-byte + comparison. This is not very compact for the case of moving data + within a page, and might be improved in the future. </para> </listitem> </itemizedlist> |