Prevent redundant copies of hash keys in string pools #1982
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Keys for cram_block_compression_hdr::TD_hash and cram_slice::pair hash tables are kept in string pools. Adding keys to the pool before putting them in the hash table could lead to redundant copies being left behind in the pool because the newly-added key was not used. To prevent this, only add keys to the string pool when the hash table entry is new, and update the hash table entry so it uses the pooled key. We can get away with this as in both cases the key is available as a NUL-terminated string that can be used for the initial hash look-up. This should slightly reduce the memory used when writing CRAM files, and remove some unnecessary memory copies.
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Keys for
cram_block_compression_hdr::TD_hashandcram_slice::pair hash tablesare kept in string pools. Adding keys to the pool before putting them in the hash table could lead to redundant copies being left behind in the pool because the newly-added key was not used. To prevent this, only add keys to the string pool when the hash table entry is new, and update the hash table entry so it uses the pooled key. We can get away with this as in both cases the key is available as a NUL-terminated string that can be used for the initial hash look-up.This will very slightly reduce the memory used when writing CRAM files, and remove some unnecessary memory copies.