H5PsetH5P_sharedSET_mesgSHARED_phaseMESG_changePHASE_CHANGE sets threshold values for storage of shared object header message indexes in a file. These phase change thresholds determine the point at which the index storage mechanism changes from a more compact list format to a more performance-oriented B-tree format, and vice-versa. By default, a shared object header message index is initially stored as a compact list. When the number of messages in an index exceeds the threshold value of max_list, storage switches to a B-tree for improved performance. If the number of messages subsequently falls below the min_btree threshold, the index will revert to the list format. If max_list is set to 0 (zero), shared object header message indexes in the file will be created as B-trees and will never revert to lists. fcpl_id specifies the file creation property list.
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