Import wiredtiger: c004346e10b186c1ecea4a1ee3186619666c9c17 from branch mongodb-master

ref: bb64c7cdca..c004346e10
for: 6.2.0-rc0

WT-7833 wt_btree_switch_object needs to coordinate with concurrent write requests to btree (#8044)

1 files changed, 9 insertions, 1 deletions

diff --git a/src/third_party/wiredtiger/src/block/block_ext.c b/src/third_party/wiredtiger/src/block/block_ext.c
index 3406f8526b2..a4451ea00e0 100644
--- a/src/third_party/wiredtiger/src/block/block_ext.c
+++ b/src/third_party/wiredtiger/src/block/block_ext.c
@@ -571,7 +571,15 @@ __wt_block_free(WT_SESSION_IMPL *session, WT_BLOCK *block, const uint8_t *addr,
     WT_RET(__wt_block_addr_unpack(
       session, block, addr, addr_size, &objectid, &offset, &size, &checksum));
 
-    /* We can't reuse free space in an object. */
+    /*
+     * Freeing blocks in a previous object isn't possible in the current architecture. We'd like to
+     * know when a previous object is either completely rewritten (or more likely, empty enough that
+     * rewriting remaining blocks is worth doing). Just knowing which blocks are no longer in use
+     * isn't enough to remove them (because the internal pages have to be rewritten and we don't
+     * know where they are); the simplest solution is probably to keep a count of freed bytes from
+     * each object in the metadata, and when enough of the object is no longer in use, perform a
+     * compaction like process to do any remaining cleanup.
+     */
     if (objectid != block->objectid)
         return (0);