If the execution of the two reads in log_t::get_lsn_approx() is
interleaved with concurrent writes of those fields in
log_t::write_buf() or log_t::persist(), the returned approximation
will be an upper bound. If log_t::append_prepare_wait() is pending,
the approximation could be a lower bound.
We must adjust each caller of log_t::get_lsn_approx() for the
possibility that the return value is larger than
MAX(oldest_modification) in buf_pool.flush_list.
af_needed_for_redo(): Add a comment that explains why the glitch
is not a problem.
page_cleaner_flush_pages_recommendation(): Revise the logic for
the unlikely case cur_lsn < oldest_lsn. The original logic would have
invoked af_get_pct_for_lsn() with a very large age value, which
would likely cause an overflow of the local variable lsn_age_factor,
and make pct_for_lsn a "random number". Based on that value,
total_ratio would be normalized to something between 0.0 and 1.0.
Nothing extremely bad should have happened in this case;
the innodb_io_capacity_max should not be exceeded.
buf_pool_t::resize(): After successfully shrinking the buffer pool,
announce the success. The size had already been updated in shrunk().
After failing to shrink the buffer pool, re-enable the adaptive
hash index if it had been enabled.
Reviewed by: Debarun Banerjee
buf_buddy_shrink(): Properly cover the case when KEY_BLOCK_SIZE
corresponds to the innodb_page_size, that is, the ROW_FORMAT=COMPRESSED
page frame is directly allocated from the buffer pool, not via the
binary buddy allocator.
buf_LRU_check_size_of_non_data_objects(): Avoid a crash when the
buffer pool is being shrunk.
buf_pool_t::shrink(): Abort if over 95% of the shrunk buffer pool
would be occupied by the adaptive hash index or record locks.
In commit b6923420f3 (MDEV-29445)
we started to specify the MAP_POPULATE flag for allocating the
InnoDB buffer pool. This would cause a lot of time to be spent
on __mm_populate() inside the Linux kernel, such as 16 seconds
to pre-fault or commit innodb_buffer_pool_size=64G.
Let us revert to the previous way of allocating the buffer pool
at startup. Note: An attempt to increase the buffer pool size by
SET GLOBAL innodb_buffer_pool_size (up to innodb_buffer_pool_size_max)
will invoke my_virtual_mem_commit(), which will use MAP_POPULATE
to zero-fill and prefault the requested additional memory area, blocking
buf_pool.mutex.
Before MDEV-29445 we allocated the InnoDB buffer pool by invoking
mmap(2) once (via my_large_malloc()). After the change, we would
invoke mmap(2) twice, first via my_virtual_mem_reserve() and then
via my_virtual_mem_commit(). Outside Microsoft Windows, we are
reverting back to my_large_malloc() like allocation.
my_virtual_mem_reserve(): Define only for Microsoft Windows.
Other platforms should invoke my_large_virtual_alloc() and
update_malloc_size() instead of my_virtual_mem_reserve() and
my_virtual_mem_commit().
my_large_virtual_alloc(): Define only outside Microsoft Windows.
Do not specify MAP_NORESERVE nor MAP_POPULATE, to preserve compatibility
with my_large_malloc(). Were MAP_POPULATE specified, the mmap()
system call would be significantly slower, for example 18 seconds
to reserve 64 GiB upfront.
A statement SET GLOBAL innodb_buffer_pool_size=...
could fail for no good reason when the buffer pool contains many
pages that can actually be evicted.
buf_flush_LRU_list_batch(): Keep evicting as long as the buffer pool
is being shrunk, for at most innodb_lru_scan_depth extra blocks.
Disregard the flush limit for pages that are marked as freed in files.
buf_flush_LRU_to_withdraw(): Update the to_withdraw target during
buf_flush_LRU_list_batch().
buf_pool_t::will_be_withdrawn(): Allow also ptr=nullptr (the condition
will not hold for it).
This fixes a regression that was introduced in
commit b6923420f3 (MDEV-29445)
and caught by the test innodb.temp_truncate_freed in MariaDB Server 11.4.
Tested by: Thirunarayanan Balathandayuthapani
Reviewed by: Thirunarayanan Balathandayuthapani
buf_buddy_alloc_from(): Pass the correct argument to
buf_pool.contains_zip(). This fixes a failure of the test
encryption.innochecksum when the code is built with
cmake -DWITH_UBSAN=ON -DCMAKE_BUILD_TYPE=Debug
The parameter innodb_log_spin_wait_delay will be deprecated and
ignored, because there is no spin loop anymore.
Thanks to commit 685d958e38
and commit a635c40648
multiple mtr_t::commit() can concurrently copy their slice of
mtr_t::m_log to the shared log_sys.buf. Each writer would allocate
their own log sequence number by invoking log_t::append_prepare()
while holding a shared log_sys.latch. This function was too heavy,
because it would invoke a minimum of 4 atomic read-modify-write
operations as well as system calls in the supposedly fast code path.
It turns out that with a simpler data structure, instead of having
several data fields that needed to be kept consistent with each other,
we only need one Atomic_relaxed<uint64_t> write_lsn_offset, on which
we can operate using fetch_add(), fetch_sub() as well as a single-bit
fetch_or(), which reasonably modern compilers (GCC 7, Clang 15 or later)
can translate into loop-free code on AMD64.
Before anything can be written to the log, log_sys.clear_mmap()
must be invoked.
log_t::base_lsn: The LSN of the last write_buf() or persist().
This is a rough approximation of log_sys.lsn, which will be removed.
log_t::write_lsn_offset: An Atomic_relaxed<uint64_t> that buffers
updates of write_to_buf and base_lsn.
log_t::buf_free, log_t::max_buf_free, log_t::lsn. Remove.
Replaced by base_lsn and write_lsn_offset.
log_t::buf_size: Always reflects the usable size in append_prepare().
log_t::lsn_lock: Remove. For the memory-mapped log in resize_write(),
there will be a resize_wrap_mutex.
log_t::get_lsn_approx(): Return a lower bound of get_lsn().
This should be exact unless append_prepare_wait() is pending.
log_get_lsn(): A wrapper for log_sys.get_lsn(), which must be invoked
while holding an exclusive log_sys.latch.
recv_recovery_from_checkpoint_start(): Do not invoke fil_names_clear();
it would seem to be unnecessary.
In many places, references to log_sys.get_lsn() are replaced with
log_sys.get_flushed_lsn(), which remains a simple std::atomic::load().
Reviewed by: Debarun Banerjee
buf_block_t::initialise(): Remove a redundant call to page.lock.init()
that was already executed in buf_pool_t::create() or
buf_pool_t::resize().
This fixes a regression that was introduced in
commit b6923420f3 (MDEV-29445).
During regular iteration the page cleaner does flush from flush list
with some flush target and then goes for generating free pages from LRU
tail. When asynchronous flush is triggered i.e. when 7/8 th of the LSN
margin is filled in the redo log, the flush target for flush list is
set to innodb_io_capacity_max. If it could flush all, the flush
bandwidth for LRU flush is currently set to zero. If the LRU tail has
dirty pages, page cleaner ends up freeing no pages in one iteration.
The scenario could repeat across multiple iterations till async flush
target is reached. During this time the DB system is starved of free
pages resulting in apparent stall and in some cases dict_sys latch
fatal error.
Fix: In page cleaner iteration, before LRU flush, ensure we provide
enough flush limit so that freeing pages is no blocked by dirty pages
in LRU tail. Log IO and flush state if double write flush wait is long.
Reviewed by: Marko Mäkelä
log_checkpoint(): In cmake -DWITH_VALGRIND=ON builds, let us
wait for all outstanding writes to complete, in order to
avoid an unexpectedly large number of innodb_log_writes
in the test innodb.page_cleaner.
recv_sys_t::wait_for_pool(): Also wait for pending writes, so that
previously written blocks can be evicted and reused.
buf_flush_sync_for_checkpoint(): Wait for pending writes, in order
to guarantee progress even if the scheduler is unfair.
innodb_buffer_pool_size_auto_min: A minimum innodb_buffer_pool_size that
a Linux memory pressure event can lead to shrinking the buffer pool to.
On a memory pressure event, we will attempt to shrink
innodb_buffer_pool_size halfway between its current value and
innodb_buffer_pool_size_auto_min. If innodb_buffer_pool_size_auto_min is
specified as 0 or not specified on startup, its default value will be
adjusted to innodb_buffer_pool_size_max, that is, memory pressure events
will be disregarded by default.
buf_pool_t::garbage_collect(): For up to 15 seconds, attempt to shrink
the buffer pool in response to a memory pressure event.
Reviewed by: Debarun Banerjee
We deprecate and ignore the parameter innodb_buffer_pool_chunk_size
and let the buffer pool size to be changed in arbitrary 1-megabyte
increments.
innodb_buffer_pool_size_max: A new read-only startup parameter
that specifies the maximum innodb_buffer_pool_size. If 0 or
unspecified, it will default to the specified innodb_buffer_pool_size
rounded up to the allocation unit (2 MiB or 8 MiB). The maximum value
is 4GiB-2MiB on 32-bit systems and 16EiB-8MiB on 64-bit systems.
This maximum is very likely to be limited further by the operating system.
The status variable Innodb_buffer_pool_resize_status will reflect
the status of shrinking the buffer pool. When no shrinking is in
progress, the string will be empty.
Unlike before, the execution of SET GLOBAL innodb_buffer_pool_size
will block until the requested buffer pool size change has been
implemented, or the execution is interrupted by a KILL statement
a client disconnect, or server shutdown. If the
buf_flush_page_cleaner() thread notices that we are running out of
memory, the operation may fail with ER_WRONG_USAGE.
SET GLOBAL innodb_buffer_pool_size will be refused
if the server was started with --large-pages (even if
no HugeTLB pages were successfully allocated). This functionality
is somewhat exercised by the test main.large_pages, which now runs
also on Microsoft Windows. On Linux, explicit HugeTLB mappings are
apparently excluded from the reported Redident Set Size (RSS), and
apparently unshrinkable between mmap(2) and munmap(2).
The buffer pool will be mapped to a contiguous virtual memory area
that will be aligned and partitioned into extents of 8 MiB on
64-bit systems and 2 MiB on 32-bit systems.
Within an extent, the first few innodb_page_size blocks contain
buf_block_t objects that will cover the page frames in the rest
of the extent. The number of such frames is precomputed in the
array first_page_in_extent[] for each innodb_page_size.
In this way, there is a trivial mapping between
page frames and block descriptors and we do not need any
lookup tables like buf_pool.zip_hash or buf_pool_t::chunk_t::map.
We will always allocate the same number of block descriptors for
an extent, even if we do not need all the buf_block_t in the last
extent in case the innodb_buffer_pool_size is not an integer multiple
of the of extents size.
The minimum innodb_buffer_pool_size is 256*5/4 pages. At the default
innodb_page_size=16k this corresponds to 5 MiB. However, now that the
innodb_buffer_pool_size includes the memory allocated for the block
descriptors, the minimum would be innodb_buffer_pool_size=6m.
my_large_virtual_alloc(): A new function, similar to my_large_malloc().
my_virtual_mem_reserve(), my_virtual_mem_commit(),
my_virtual_mem_decommit(), my_virtual_mem_release():
New interface mostly by Vladislav Vaintroub, to separately
reserve and release virtual address space, as well as to
commit and decommit memory within it.
After my_virtual_mem_decommit(), the virtual memory range will be
read-only or unaccessible, depending on whether the build option
cmake -DHAVE_UNACCESSIBLE_AFTER_MEM_DECOMMIT=1
has been specified. This option is hard-coded on Microsoft Windows,
where VirtualMemory(MEM_DECOMMIT) will make the memory unaccessible.
On IBM AIX, Linux, Illumos and possibly Apple macOS, the virtual memory
will be zeroed out immediately. On other POSIX-like systems,
madvise(MADV_FREE) will be used if available, to give the operating
system kernel a permission to zero out the virtual memory range.
We prefer immediate freeing so that the reported
resident set size (RSS) of the process will reflect the current
innodb_buffer_pool_size. Shrinking the buffer pool is a rarely
executed resource intensive operation, and the immediate configuration
of the MMU mappings should not incur significant additional penalty.
opt_super_large_pages: Declare only on Solaris. Actually, this is
specific to the SPARC implementation of Solaris, but because we
lack access to a Solaris development environment, we will not revise
this for other MMU and ISA.
buf_pool_t::chunk_t::create(): Remove.
buf_pool_t::create(): Initialize all n_blocks of the buf_pool.free list.
buf_pool_t::allocate(): Renamed from buf_LRU_get_free_only().
buf_pool_t::LRU_warned: Changed to Atomic_relaxed<bool>,
only to be modified by the buf_flush_page_cleaner() thread.
buf_pool_t::shrink(): Attempt to shrink the buffer pool.
There are 3 possible outcomes: SHRINK_DONE (success),
SHRINK_IN_PROGRESS (the caller may keep trying),
and SHRINK_ABORT (we seem to be running out of buffer pool).
While traversing buf_pool.LRU, release the contended
buf_pool.mutex once in every 32 iterations in order to
reduce starvation. Use lru_scan_itr for efficient traversal,
similar to buf_LRU_free_from_common_LRU_list().
buf_pool_t::shrunk(): Update the reduced size of the buffer pool
in a way that is compatible with buf_pool_t::page_guess(),
and invoke my_virtual_mem_decommit().
buf_pool_t::resize(): Before invoking shrink(), run one batch of
buf_flush_page_cleaner() in order to prevent LRU_warn().
Abort if shrink() recommends it, or no blocks were withdrawn in
the past 15 seconds, or the execution of the statement
SET GLOBAL innodb_buffer_pool_size was interrupted.
buf_pool_t::first_to_withdraw: The first block descriptor that is
out of the bounds of the shrunk buffer pool.
buf_pool_t::withdrawn: The list of withdrawn blocks.
If buf_pool_t::resize() is aborted before shrink() completes,
we must be able to resurrect the withdrawn blocks in the free list.
buf_pool_t::contains_zip(): Added a parameter for the
number of least significant pointer bits to disregard,
so that we can find any pointers to within a block
that is supposed to be free.
buf_pool_t::is_shrinking(): Return the total number or blocks that
were withdrawn or are to be withdrawn.
buf_pool_t::to_withdraw(): Return the number of blocks that will need to
be withdrawn.
buf_pool_t::usable_size(): Number of usable pages, considering possible
in-progress attempt at shrinking the buffer pool.
buf_pool_t::page_guess(): Try to buffer-fix a guessed block pointer.
If HAVE_UNACCESSIBLE_AFTER_MEM_DECOMMIT is set, the pointer will
be validated before being dereferenced.
buf_pool_t::get_info(): Replaces buf_stats_get_pool_info().
innodb_init_param(): Refactored. We must first compute
srv_page_size_shift and then determine the valid bounds of
innodb_buffer_pool_size.
buf_buddy_shrink(): Replaces buf_buddy_realloc().
Part of the work is deferred to buf_buddy_condense_free(),
which is being executed when we are not holding any
buf_pool.page_hash latch.
buf_buddy_condense_free(): Do not relocate blocks.
buf_buddy_free_low(): Do not care about buffer pool shrinking.
This will be handled by buf_buddy_shrink() and
buf_buddy_condense_free().
buf_buddy_alloc_zip(): Assert !buf_pool.contains_zip()
when we are allocating from the binary buddy system.
Previously we were asserting this on multiple recursion levels.
buf_buddy_block_free(), buf_buddy_free_low():
Assert !buf_pool.contains_zip().
buf_buddy_alloc_from(): Remove the redundant parameter j.
buf_flush_LRU_list_batch(): Add the parameter to_withdraw
to keep track of buf_pool.n_blocks_to_withdraw.
buf_do_LRU_batch(): Skip buf_free_from_unzip_LRU_list_batch()
if we are shrinking the buffer pool. In that case, we want
to minimize the page relocations and just finish as quickly
as possible.
trx_purge_attach_undo_recs(): Limit purge_sys.n_pages_handled()
in every iteration, in case the buffer pool is being shrunk
in the middle of a purge batch.
Reviewed by: Debarun Banerjee
- InnoDB fails to recover the full crc32 page_compressed page
from doublewrite buffer. The reason is that buf_dblwr_t::recover()
fails to identify the space id from the page because the page
has compressed from FIL_PAGE_FILE_FLUSH_LSN_OR_KEY_VERSION bytes.
Fix:
===
recv_dblwr_t::find_deferred_page(): Find the page which
has the same page number and try to decompress/decrypt the page
based on the tablespace metadata. After the decompression/decryption,
compare the space id and write the recovered page back to the file.
buf_page_t::read_complete(): Page read from disk is corrupted then
try to read the page from deferred pages in doublewrite buffer.
Currently it is allowed to set innodb_io_capacity to very large value
up to unsigned 8 byte maximum value 18446744073709551615. While
calculating the number of pages to flush, we could sometime go beyond
innodb_io_capacity. Specifically, MDEV-24369 has introduced a logic
for aggressive flushing when dirty page percentage in buffer pool
exceeds innodb_max_dirty_pages_pct. So, when innodb_io_capacity is
set to very large value and dirty page percentage exceeds the
threshold, there is a multiplication overflow in Innodb page cleaner.
Fix: We should prevent setting io_capacity to unrealistic values and
define a practical limit to it. The patch introduces limits for
innodb_io_capacity_max and innodb_io_capacity to the maximum of 4 byte
unsigned integer i.e. 4294967295 (2^32-1). For 16k page size this limit
translates to 64 TiB/sec write IO speed which looks sufficient.
Reviewed by: Marko Mäkelä
log_t::writer_update(): Add the parameter bool resizing,
to indicate whether log resizing is in progress.
We must enable log_writer_resizing only if resize_lsn>1,
to ensure that log_t::resize_abort() will not choose the wrong
log_sys.log_writer.
log_t::resize_initiator: The thread that successfully invoked
resize_start().
log_t::resize_start(): Simplify some logic, and assign resize_initiator
if we successfully started log resizing.
log_t::resize_abort(): Abort log resizing if we are the
resize_initiator.
innodb_log_file_size_update(): Clean up some logic.
Reviewed by: Debarun Banerjee
Most InnoDB functions do not throw any exceptions, not even indirectly
std::bad_alloc, which could be thrown by a C++ memory allocation function.
Let us annotate many functions with noexcept in order to reduce the code
footprint related to exception handling.
Reviewed by: Thirunarayanan Balathandayuthapani
- InnoDB fails to recover the full crc32 encrypted page from
doublewrite buffer. The reason is that buf_dblwr_t::recover()
fails to identify the space id from the page because the page has
been encrypted from FIL_PAGE_FILE_FLUSH_LSN_OR_KEY_VERSION bytes.
Fix:
===
buf_dblwr_t::recover(): preserve any pages whose space_id
does not match a known tablespace. These could be encrypted pages
of tablespaces that had been created with
innodb_checksum_algorithm=full_crc32.
buf_page_t::read_complete(): If the page looks corrupted and the
tablespace is encrypted and in full_crc32 format, try to
restore the page from doublewrite buffer.
recv_dblwr_t::recover_encrypted_page(): Find the page which
has the same page number and try to decrypt the page using
space->crypt_data. After decryption, compare the space id.
Write the recovered page back to the file.
In function buf_page_create_low(), remove duplicate code that
over-write the ibuf_exist variable incorrectly when only compressed
page is loaded in buffer pool. This would help removing any old change
buffer record immediately before re-using the page.
If InnoDB is killed in such a way that there had been no writes
to a newly resized ib_logfile101 after it replaced ib_logfile0
in log_t::write_checkpoint(), it is possible that recovery will
accidentally interpret some garbage at the end of the log as valid.
log_t::write_buf(): To prevent the corruption, write an extra NUL byte
at the end of log_sys.resize_buf, like we always did for the main
log_sys.buf. To remove some conditional branches from a time critical
code path, we instantiate a separate template for the rare case that the
log is being resized. Define as __attribute__((always_inline)) so that
this will be inlined also in the rare case the log is being resized.
log_t::writer: Pointer to the current implementation of
log_t::write_buf(). For quick access, this is located in the
same cache line with log_sys.latch, which protects it.
log_t::writer_update(): Update log_sys.writer.
log_t::resize_write_buf(): Remove ATTRIBUTE_NOINLINE ATTRIBUTE_COLD.
Now that log_t::write_buf() will be instantiated separately for the
rare case of log resizing being in progress, there is no need to forbid
this code from being inlined.
Thanks to Thirunarayanan Balathandayuthapani for finding the
root cause of this bug and suggesting the fix of writing an extra
NUL byte.
Reviewed by: Debarun Banerjee
This regression is introduced in 10.6 by following commit.
commit 35d477dd1d
MDEV-34453 Trying to read 16384 bytes at 70368744161280
The page state could change after being buffer-fixed and needs to be
read again after locking the page.
Under unknown circumstances, the SQL layer may wrongly disregard an
invocation of thd_mark_transaction_to_rollback() when an InnoDB
transaction had been aborted (rolled back) due to one of the following errors:
* HA_ERR_LOCK_DEADLOCK
* HA_ERR_RECORD_CHANGED (if innodb_snapshot_isolation=ON)
* HA_ERR_LOCK_WAIT_TIMEOUT (if innodb_rollback_on_timeout=ON)
Such an error used to cause a crash of InnoDB during transaction commit.
These changes aim to catch and report the error earlier, so that not only
this crash can be avoided but also the original root cause be found and
fixed more easily later.
The idea of this fix is from Michael 'Monty' Widenius.
HA_ERR_ROLLBACK: A new error code that will be translated into
ER_ROLLBACK_ONLY, signalling that the current transaction
has been aborted and the only allowed action is ROLLBACK.
trx_t::state: Add TRX_STATE_ABORTED that is like
TRX_STATE_NOT_STARTED, but noting that the transaction had been
rolled back and aborted.
trx_t::is_started(): Replaces trx_is_started().
ha_innobase: Check the transaction state in various places.
Simplify the logic around SAVEPOINT.
ha_innobase::is_valid_trx(): Replaces ha_innobase::is_read_only().
The InnoDB logic around transaction savepoints, commit, and rollback
was unnecessarily complex and might have contributed to this
inconsistency. So, we are simplifying that logic as well.
trx_savept_t: Replace with const undo_no_t*. When we rollback to
a savepoint, all we need to know is the number of undo log records
that must survive.
trx_named_savept_t, DB_NO_SAVEPOINT: Remove. We can store undo_no_t
directly in the space allocated at innobase_hton->savepoint_offset.
fts_trx_create(): Do not copy previous savepoints.
fts_savepoint_rollback(): If a savepoint was not found, roll back
everything after the default savepoint of fts_trx_create().
The test innodb_fts.savepoint is extended to cover this code.
Reviewed by: Vladislav Lesin
Tested by: Matthias Leich
buf_dblwr_t::recover(): Correct a debug assertion failure that had
been added in commit bb47e575de (MDEV-34830).
The server may have been killed while a log write was in progress, and
therefore recv_sys.scanned_lsn may be up to RECV_PARSING_BUF_SIZE bytes
ahead of recv_sys.recovered_lsn.
Thanks to Matthias Leich for providing "rr replay" traces and
testing this.
fil_space_t::create(): Instead of invoking the default fil_space_t
constructor on a zero-filled buffer, allocate an uninitialized buffer
and invoke an explicitly defined constructor on it. Also, specify
initializer expressions for all constant data members, so that all of them
will be initialized in the constructor.
fil_space_t::being_imported: Replaces part of fil_space_t::purpose.
fil_space_t::is_being_imported(), fil_space_t::is_temporary():
Replaces fil_space_t::purpose.
fil_space_t:🆔 Changed the type from ulint to uint32_t to reduce
incompatibility with later branches that include
commit ca501ffb04 (MDEV-26195).
fil_space_t::try_to_close(): Do not attempt to close files that are
in an I/O bound phase of ALTER TABLE…IMPORT TABLESPACE.
log_file_op, first_page_init: recv_spaces_t:
Use uint32_t for the tablespace id.
Reviewed by: Debarun Banerjee
buf_block_alloc(): Define as an alias in buf0lru.h, which defines
the underlying buf_LRU_get_free_block().
buf_block_free(): Define as an alias of the non-inline function
buf_pool.free_block(block).
Reviewed by: Vladislav Lesin
A race condition was observed between two buf_page_get_zip() for a page.
One of them had proceeded to buf_read_page(), allocating and x-latching
a buf_block_t that initially comprises only an uncompressed page frame.
While that thread was waiting inside buf_block_alloc(), another thread
would try to access the same page. Without acquiring a page latch, it
would wrongly conclude that there is corruption because no compressed
page frame exists for the block.
buf_page_get_zip(): Simplify the logic and correct the documentation.
Always acquire a shared latch to prevent any race condition with a
concurrent read operation. No longer increment a buffer-fix; the latch
is sufficient for preventing page relocation or eviction.
buf_read_page(): Add the parameter bool unzip=true. In buf_page_get_zip()
there is no need to allocate an uncompressed page frame for reading a
compressed BLOB page. We only need that for other ROW_FORMAT=COMPRESSED
pages, or for writing compressed BLOB pages.
btr_copy_zblob_prefix(): Remove the message "Cannot load compressed BLOB"
because buf_page_get_zip() will already have reported a more specific
error whenever it returns nullptr.
row_merge_buf_add(): Do not crash on BLOB corruption, but return an
error instead. (In debug builds, an assertion will fail if this
corruption is noticed.)
Reviewed by: Debarun Banerjee
