There are still some bugs in the code.

btr_store_big_rec_extern_fields(): Remove assertion on dict_table_is_zip()
to ease testing.

btr_free_externally_stored_field(): Test page_zip instead of
dict_table_is_zip().

page_zip_write_rec(): Add parameter "create".  Try to handle externally
stored columns.

rec_offs_any_extern(): Correct the function comment.

Add rec_offs_n_extern() and page_zip_get_n_prev_extern().

page_zip_dir_decode(): Replace assertion with if (...) return(FALSE).

page_zip_decompress(): Do not clear page_zip->n_blobs after counting the
BLOBs.

page_zip_write_blob_ptr(): Use page_zip_get_n_prev_extern().
Correct an off-by-one error in memcpy().

btr_cur_pessimistic_update(): Remove extraneous page_zip_write_rec() call.

btr_cur_set_ownership_of_extern_field(): Simplify the logic.

row_upd_rec_in_place(): Make use of parameter "index" in debug assertions.

page_zip_write_rec(): Remove TODO comment about redo log record.
The write will already be covered by higher-level log entries.

buf_block_align(btr_cur_get_rec()).

btr_compress(): Pass the correct page_zip to btr_node_ptr_set_child_page_no().

page_mem_free(): Remove parameter mtr.  Do not call page_zip_clear_rec() here.

page_cur_delete_rec(): Call page_zip_clear_rec() here.  Decrement PAGE_N_RECS
only after calling page_mem_free().  Assert page_zip_validate().

of clustered indexes.  Previously, parts of the code assumed that these
columns would exist on all leaf pages.  Simplify the update-in-place of
these columns.

Add inline function dict_index_is_clust() to replace all tests
index->type & DICT_CLUSTERED.

Remove the redo log entry types MLOG_ZIP_WRITE_TRX_ID and
MLOG_ZIP_WRITE_ROLL_PTR, because the modifications to these columns
are covered by logical logging.

Fuse page_zip_write_trx_id() and page_zip_write_roll_ptr() into
page_zip_write_trx_id_and_roll_ptr().

page_zip_dir_add_slot(), page_zip_available(): Add flag "is_clustered",
so that no space will be reserved for TRX_ID and ROLL_PTR on leaf pages
of secondary indexes.

page_zip_apply_log(): Flag an error when val==0 is encoded with two bytes.

page_zip_write_rec(): Add debug assertions that there is enough space
available for the entry before copying the data bytes of the record.

btr_cur_update_in_place(): Remove the page_zip_write_rec() call,
because row_upd_rec_in_place() already calls it.

page_dir_split_slot(): Do not pass page_zip to page_dir_slot_set_n_owned(),
because the caller will rewrite the dense page directory later.  At this
point of execution, the dense directory will not contain the newly inserted
record, which may end up being written to new_slot.

btr_root_raise_and_insert(): Because btr_page_set_level() must not
change level from non-zero to zero on compressed pages, invoke
btr_page_set_level() with page_zip==NULL and compress the entire
root page after creating it from the scratch.

btr_attach_half_pages(): Simplify the computation of lower_page_zip
and upper_page_zip.  Invoke btr_node_ptr_set_child_page_no() with
the correct page_zip.

page0page.h: Add __attribute__((const)) to functions testing for
infimum or supremum.

page_zip_dir_delete(): Note that the third parameter may be NULL.
Correct offset errors.

page_zip_available(): Use n_heap instead of n_recs.

page_zip_dir_find(), page_zip_dir_find_free(): Fix off-by-one error.

page_zip_fields_encode(), page_zip_fields_decode(): Encode and decode
index->n_nullable for non-leaf pages.

page_zip_apply_log(): Write REC_NEW_HEAP_NO before calling
rec_offs_make_valid().

page_zip_write_node_ptr(): Correct off-by-one error.

page_cur_search_with_match(): Make use of page_is_leaf().

page_dir_add_slots(): Replaced with page_dir_add_slot().  Use memmove().

before and after the operation.

buf_flush_init_for_writing(): Copy FIL_PAGE_LSN to the compressed page.

page_cur_insert_rec_low(): Add debug assertion.

page_zip_fixed_field_encode(), page_zip_fields_encode(),
page_zip_fields_decode(): Do not waste one bit when encoding quantities
larger than 127.

page_zip_apply_log(), page_zip_write_rec(): Decode and encode
heap_no >= 127 correctly.

page_zip_apply_log(): Correct an off-by-one error.

page_zip_write_rec(): Correct a debug assertion.
Encode heap_no as soon as possible.

row_upd_rec_in_place(), page_zip_write_rec(): Add parameter "index".

page_dir_set_n_heap(): Add a debug assertion that on compressed
pages, n_heap will always be incremented by one.  Improve code formatting.

page_zip_dir_add_slot(): New function, called from
page_cur_insert_rec_low() after page_mem_alloc_heap().

rec_set_n_owned_new(): Do not call page_zip_rec_set_owned()
on the supremum record.

rec_offs_make_valid(): Add debug assertions.

page_zip_dir_user_size(): Correct an off-by-one error in the debug assertion.

page_zip_apply_log(): Add parameter trx_id_col.  Skip trx_id and roll_ptr.

page_zip_decompress(): Simplify the handling of "storage" in the loop that
copies the uncompressed fields.

page_zip_write_rec(): Store trx_id and roll_ptr separately.

page_zip_write_trx_id(), page_zip_write_roll_ptr(): Fix off-by-one errors.

page_cur_insert_rec_low(): Call page_zip_dir_add_slot() after
page_mem_alloc_heap().  Remove some redundant assertions.
Pass page_zip to page_dir_split_slot().

rec_get_offsets_reverse(): Calculate extra_size correctly.

page_zip_apply_log(): Fix an off-by-one error in comparison.
Replace heap_status with hs where possible.
Increment the heap_no in heap_status correctly.

page_zip_decompress(): Eliminate the local variable "err".
Check for Z_STREAM_END only at the start of a record, so that
incomplete records will always be detected.

page_zip_write_rec(): Calculate the address of "storage" in the
same way as elsewhere.  Add TODO comments regarding the handling
of the uncompressed fields (BLOB pointers, trx_id, and roll_ptr).

btr_create(): page_zip_compress() returns FALSE on failure.

page_zip_write_header(): Write to page_zip->data[] instead of page_zip[].

buf_flush_init_for_writing(): Add parameter page_zip and set the fields
also in the header of the compressed page.

btr_cur_search_to_nth_level(): Add ut_ad() on page_zip_validate().

page_zip_compress(), page_zip_decompress(), page_zip_write_rec():
Note that the end marker of the modification log is 1 byte.

page_zip_find_heap_no(): Remove.

page_zip_apply_log(): Remove parameter "page".  Instead of a 2-byte offset
to the record, decode the heap number using a variable-length code.

page_zip_write_rec(): Check the range of heap_no with debug assertions.
Encode the heap number instead of an offset to the start of the record.

to page0zip.c.

function prototypes and comments.  These changes were accidentally
forgotten from revision 253.

operation succeeds.

page_zip_dir_set(): Remove, as the slots will be written to a temporary
buffer.

page_zip_dir_encode(): Replace page_zip with buf.  Make some assertions
more accurate.  Write the dense page directory to buf.

page_zip_compress(): Allocate a temporary buffer for the compressed page
except the page header.  Make some assertions more accurate.

page_zip_compress(), page_zip_decompress(): Remove 2 bytes of empty space
adjacent to the area reserved for storing uncompressed columns.

page_zip_decompress(): Free index and heap at the end of the function.
Do not write the index to the MLOG_ZIP_DECOMPRESS record, since it can be
decoded from the compressed page.

now that deletion of records on compressed pages is guaranteed to succeed.

on a compressed page.

page_zip_get_n_relocated(), page_zip_set_n_relocated(),
page_zip_get_relocated(): Remove.

page0zip.c, page0zip.ic: Remove all references to n_relocated.

page_cur_insert_rec_low(): On pages that are compressed,
never relocate records that are allocated from the free list.

page_zip_compress(): Add assertions !c_stream.avail_in where appropriate.
Add assertions on c_stream.next_in.  Correct malformed assertion on
externs > c_stream.next_in.  Note that there may be trailing garbage after
the last record.

page_zip_fields_decode(): Correctly decode variable-length fields having
maximum length greater than 255 bytes.

page_zip_decompress(): Remove the special treatment of the case !n_dense.
Replace the Z_NO_FLUSH argument of inflate() with Z_SYNC_FLUSH.
Treat Z_OK return value the same as Z_BUF_ERROR: always check avail_out.
After decompressing all records, decompress any trailing garbage.

page_cur_insert_rec_low(): Note that the relocation log
on the compressed page needs to reflect some changes of extra_size.

do not allow extra_size to decrease on compressed pages.

Split page_mem_alloc() to page_mem_alloc_free() and page_mem_alloc_heap().

page_cur_insert_rec_low(): Remove parameter "tuple".  Implement some of the
logic from page_mem_alloc().

page_cur_tuple_insert(): Convert the tuple to a record and calculate offsets.

page_zip_validate(): Assert that the page is in compact format.

Remove the declaration of the undefined function
page_zip_available_noninline().

Make page_zip_available() private to page0zip.c and page0zip.ic.

compressed pages.

btr_root_raise_and_insert(): Distinguish root_page_zip and new_page_zip.

btr_cur_set_ownership_of_extern_field(): Do not log the write on the
uncompressed page if it will be logged for page_zip.

lock_rec_insert_check_and_lock(), lock_sec_rec_modify_check_and_lock():
Update the max_trx_id field also on the compressed page.

mlog_write_ulint(): Add UNIV_UNLIKELY hints.  Remove trailing white space.

mlog_log_string(): Remove trailing white space.

rec_set_field_extern_bits(): Remove parameter mtr, as the write will either
occur in the heap, or it will be logged at a higher level.

recv_parse_or_apply_log_rec_body(),
page_zip_write_header(): Add log record type MLOG_ZIP_WRITE_HEADER.

page_header_set_field(): Pass mtr=NULL to page_zip_write_header().

page_header_reset_last_insert(): Pass mtr to page_zip_write_header().

btr_page_set_index_id(), btr_page_set_level(),
btr_page_set_next(), btr_page_set_prev(): Pass mtr to page_zip_write_header().

row_upd_rec_sys_fields(): Pass mtr=NULL to page_zip_write_trx_id() and
page_zip_write_roll_ptr(), since the write will be logged at a higher level.

page_zip_write_header(): Add parameter mtr.
page_zip_write_header_log(): New function.

Remove rec_set_nth_field_extern_bit().
Make rec_set_nth_field_extern_bit_old() static.
Rename rec_set_nth_field_extern_bit_new()
to rec_set_field_extern_bits_new() and make it static.

row_ins_index_entry_low(): Remove bogus TODO comment.

dict_mem_table_create(): Initialize table->zip.

btr0cur.c: Distinguish compressed BLOBs based on page_zip or table->zip.

Fix the way how btr_free_externally_stored_field() is called in purge.

btr_free_externally_stored_field(): Add parameter field_ref that points
directly to the BLOB reference.  Use rec, offsets, page_zip, and i
only for the page_zip_write_blob_ptr() call.

row_purge_upd_exist_or_extern(): Do not assume that the undo log contains
the entire record.  Only pass the BLOB reference to
btr_free_externally_stored_field().

btr_cur_pessimistic_insert(): Pass the "extern storage" flags to
btr_root_raise_and_insert() or btr_page_split_and_insert().

btr_copy_externally_stored_field(): Include local_len in the returned length.

btr_cur_optimistic_insert(): Replace page_cur_insert_rec_low()
with page_cur_tuple_insert().

btr_cur_pessimistic_update(): Add the columns of big_rec_vec to ext_vect,
so that the "extern storage" bits will be set correctly in
btr_cur_insert_if_possible().