Bug #30417719 ASSERTION FAILURE: FSP0FSP.CC:2371:N_USED_NOT_FULL > 0 || N_TOTAL_NOT_FULL == 0

This is the second post push fix.  The test innodb.virtual_basic was failing.
The case where the LOB was already purged needed to be handled explicitly.

rb#23522

Author: gurusami

storage/innobase/include/lob0lob.h

@@ -178,6 +178,12 @@ struct ref_mem_t {
 
   /** Whether the blob is being modified. */
   bool m_being_modified;
+
+  /** Check if the LOB has already been purged.
+  @return true if LOB has been purged, false otherwise. */
+  bool is_purged() const {
+    return ((m_page_no == FIL_NULL) && (m_length == 0));
+  }
 };
 
 extern const byte field_ref_almost_zero[FIELD_REF_SIZE];

storage/innobase/lob/lob0lob.cc

@@ -1220,6 +1220,11 @@ void ref_t::mark_not_partially_updatable(trx_t *trx, mtr_t *mtr,
 
   parse(ref_mem);
 
+  /* If LOB has already been purged, ignore it. */
+  if (ref_mem.is_purged()) {
+    return;
+  }
+
   block = buf_page_get(page_id_t(ref_mem.m_space_id, ref_mem.m_page_no),
                        page_size, RW_X_LATCH, mtr);
 

storage/innobase/lob/lob0purge.cc

@@ -425,15 +425,18 @@ void purge(DeleteContext *ctx, dict_index_t *index, trx_id_t trxid,
     mtr_commit(&lob_mtr);
   }
 
+  if (!ctx->is_ref_valid()) {
+    /* The LOB reference has changed.  Don't proceed. */
+    return;
+  }
+
   /* If rec_type is 0, it is not the purge operation. */
   if (!is_rollback && rec_type != 0 && !ctx->is_delete_marked()) {
     /* This is the purge operation. The delete marked clustered record has been
     reused. Purge shouldn't proceed. */
     return;
   }
 
-  ut_ad(ctx->is_ref_valid());
-
   space_id_t space_id = ref.space_id();
   ut_ad(space_id == index->space_id());
   page_no_t first_page_no = ref.page_no();