postgres.git / summary / log / commit / refs

commit    236f1ea84c4ca6a29d790fac4b48eba12a74443c
Author:   Heikki Linnakangas <heikki.linnakangas@iki.fi>
Date:     Mon Jan 23 09:56:43 2023 +0000
First released in: 16.0, 15.2

    Fix and clarify function comment on LogicalTapeSetCreate.
    
    Commit c4649cce39 removed the "shared" and "ntapes" arguments, but the
    comment still talked about "shared". It also talked about "a shared
    file handle", which was technically correct because even before commit
    c4649cce39, the "shared file handle" referred to the "fileset"
    argument, not "shared". But it was very confusing. Improve the
    comment.
    
    Also add a comment on what the "preallocate" argument does.
    
    Backpatch to v15, just to make backpatching other patches easier in
    the future.
    
    Discussion: https://www.postgresql.org/message-id/af989685-91d5-aad4-8f60-1d066b5ec309@enterprisedb.com
    Reviewed-by: Peter Eisentraut


 src/backend/utils/sort/logtape.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/src/backend/utils/sort/logtape.c b/src/backend/utils/sort/logtape.c
index 56ac0298c55..64ea237438b 100644
--- a/src/backend/utils/sort/logtape.c
+++ b/src/backend/utils/sort/logtape.c
@@ -537,14 +537,20 @@ ltsInitReadBuffer(LogicalTape *lt)
  * The tape set is initially empty. Use LogicalTapeCreate() to create
  * tapes in it.
  *
- * Serial callers pass NULL argument for shared, and -1 for worker.  Parallel
- * worker callers pass a shared file handle and their own worker number.
+ * In a single-process sort, pass NULL argument for fileset, and -1 for
+ * worker.
  *
- * Leader callers pass a shared file handle and -1 for worker. After creating
- * the tape set, use LogicalTapeImport() to import the worker tapes into it.
+ * In a parallel sort, parallel workers pass the shared fileset handle and
+ * their own worker number.  After the workers have finished, create the
+ * tape set in the leader, passing the shared fileset handle and -1 for
+ * worker, and use LogicalTapeImport() to import the worker tapes into it.
  *
  * Currently, the leader will only import worker tapes into the set, it does
  * not create tapes of its own, although in principle that should work.
+ *
+ * If preallocate is true, blocks for each individual tape are allocated in
+ * batches.  This avoids fragmentation when writing multiple tapes at the
+ * same time.
  */
 LogicalTapeSet *
 LogicalTapeSetCreate(bool preallocate, SharedFileSet *fileset, int worker)


[parent: 67c5b8840fca]