path: root/NEWS

WiredTiger release 1.3.5, 2012-10-26
------------------------------------

This is a bugfix and performance tuning release. The changes are as follows:

[#370] Document that applications are responsible for figuring out their
       upgrade path if they might swap out compression engines.

[#371] When a single session was used to reconcile multiple btrees, one of
       which had dictionaries configured and one of which didn't, we failed to
       clear the dictionary when starting page reconciliation.   Be consistent,
       never use anything other than the btree handle's configuration to decide
       if we're using a dictionary in a reconcilation run.

[#372] Fix several potential integer overflow bugs.

[#373] Fix a bug where calls that performed an operation on multiple objects
       (such as creating a table that implicitly creates a column group)
       could leave the metadata incomplete if a process exited without
       calling `WT_CONNECTION::close`.
       Hold the schema lock while opening tables. Fixes the error "cannot be
       opened until all column groups are created" message when create calls
       race with open_cursor.

[#374] Fix a race that caused crashes when using the Python API with
       multi-threaded code.

[#375] Fix a bug in __wt_cond_wait - so that it returns after timeout expires.

* Protect the list of LSM trees with the schema lock to avoid races during
  create.

* Update ex_test_perf to output statistics during populate and improve timing
  accuracy.

* Skew eviction in favor of leaf pages - which improves read-only performance
  for large LSM trees.

* Hold the LSM tree lock while gathering statistics.

* Fix a bug in bulk load of bitmap files.

* Fix a related bug in the bloom code that uses bitmap stores.

* Don't attempt to drop the first chunk of an LSM tree before creating it.

* Instead of entering a fake key cell after the last cell on the page just
  in case the page ends with a key cell which has no value, use the end of
  the page to detect that case.

* Cache cursor key/value formats in Python, to save a native call from every
  get_key/value.

* Don't sync the directory after open if the global "sync" flag is false.

* Fix a race for LSM trees that could happen if two threads race to open a
  cursor and drop the LSM tree.

WiredTiger release 1.3.4, 2012-10-19
------------------------------------

This release includes several important new features, including:

* support for online compaction of files;
* support for tables, column groups and indices that use LSM trees for
  storage; and
* improved statistics and configuration for LSM trees and Bloom filters.

In addition, there are some significant performance improvements and bug
fixes.  The full list of changes is:

[#248]	Add support for online compaction.

[#310]	Fixed a bug where overflow blocks could be accessed by a
	long-running reader after they had been freed in a checkpoint.

[#358]	Allocate checkpoint blocks from the live system's list of available
	blocks rather than always extending the file.

[#361]	Sync the directory after creating a file: this is apparently
	required for durability on Linux, according to the Linux fsync man
	page.

[#362]	Don't check if a page is on the avail or discard lists if we're
	salvaging the file, that is okay.

[#363]	Remove obsolete code dealing with forced eviction.

[#366]	Fake checkpoints may have the delete flag set, ignore them when
	rolling checkpoints forward.

[#367]	All metadata reads should ignore the application's transactional
	context.

[#369]	Support LSM as a data source for tables, column groups and indices.

* Add tuning options for LSM bloom filters, including controlling whether
  the oldest level in the tree has a Bloom filter, whether newly-created
  (level 0) files have Bloom filters, and passing arbitrary file
  configuration for Bloom filters.

* Add a merge generation to LSM chunks.  Add a statistic that reports the
  highest merge generation in a tree.

* Add a new LSM statistic tracking searches that could benefit from bloom
  filters.

* Enable LSM statistics in the "wt stat" utility.

* Interrupt LSM merge operations, rather than waiting on close.

* Wait for a while before looking for LSM major merges, in case merges
  catch up with inserts.

* Fix LSM index searches.  The main issue was LSM search_near was not
  always returning the closest key to the search key, which calling code
  expects.  It now tries hard to find the smallest cursor larger than the
  search key, and only if no larger record exists does it return the
  largest record smaller than the search key.

* Reset any old cursor position before an LSM search.  This limits hazard
  references in an LSM search to a single chunk.

* Fix a memory leak in an error path in Bloom filters.

* Tweak the search loops in hazard_{set,clear} in favor of
  last-in-first-out ordering.

* If there are many files open, some hotter than others, walk more files
  looking for pages to evict.

* Don't stop evicting until we reach the target, have eviction wake up
  periodically regardless of whether the application signals it.  This
  latter requires a "timed condition wait" operation.

* Tweaks to file handle flags for out-of-cache read performance on Linux
  (disable readahead and access time updates).

* Replace the WT_SESSION::dumpfile method with configuration strings to
  WT_SESSION::verify.

* Fix a bug where we weren't skipping unnecessary default checkpoints
  because we weren't handling the generational number included in the
  internal checkpoint name.

* Add a "force" configuration flag to WT_SESSION::checkpoint, object
  compaction needs it because the work it wants done is done by the block
  manager.

* Make compact and checkpoint operate on a table's indices.

* When doing a page truncate, lock down the page before we unpack the
  on-page cell -- it's possible the page could be instantiated, modified
  and reconciled while we're sleeping, in which case the WT_REF.addr field
  would no longer point on-page.


WiredTiger release 1.3.3, 2012-10-11
------------------------------------

This is a bugfix and performance tuning release, primarily related to LSM
trees.  The changes are as follows:

[#350] Checkpoint the metadata after successful schema-level operations.
       Otherwise, if process exits without closing the connection or
       running a checkpoint, created objects exist but there is no record
       in the metadata.

[#351] Don't put checkpoint extent blocks on the available list, blocks on
       it are considered for truncation; they have to go on the "checkpoint
       available" list.

* Choose LSM merges based on a measure of efficiency (levels collapsed per
  record), rather than simply choosing a minor or a major merge.  Tweak the
  merge heuristic so we don't end up with runs of smaller chunks in the
  middle of the tree.

* Add a connection-wide flag to disable LSM merges.

* Don't create Bloom filters for the oldest chunk in the system.  Add the
  ability to disable Bloom filters entirely.

* Fix fast-path for bit values in WT_CURSOR::set_value.

* Clean up allocation of LSM chunk IDs.

* Update bloom_get so that it doesn't hold a cursor position.

* Respect the page size for fixed-length column stores, remembering there
  are 8 bits per byte.

* Support bulk loading a bitmap into a fixed-length column store, update
  Bloom filter code to use this.

* Add an example program, ex_test_perf, to demonstrate basic LSM usage.

* Add a new statistics cursor type "statistics:lsm".  Update ex_stat.c to
  demonstrate usage.

* Add a statistics_fast flag to file statistics cursors.  Update LSM
  statistics so that they aggregate some cache statistics.  Add ability to
  open a statistics cursor on a checkpoint.

* Walk a constant number of pages for LRU eviction.

* Move the cache full check to after an update operation completes, when it
  is no longer holding hazard references.  This improves behavior with
  small caches.


WiredTiger release 1.3.2, 2012-10-03
------------------------------------

This is a bugfix and performance tuning release, primarily related to LSM
trees.  The changes are as follows:

* Implement minor merges for LSM trees, prefer them to major merges.

* Update hazard references, so the active array grows as needed.  Change
  the default hazard_max to 1000.

* Abort transactions if the cache is so full that they cannot make
  progress.

* Fix a bug where verify could crash if an empty checkpoint exists.

* Make the maximum number of chunks for merges configurable, rather than
  deriving a value from the number of hazard references available.

* Switch to an atomic add to allocate transaction IDs.  This fixes a subtle
  race before where two threads could temporarily have the same ID in the
  global state table.  If one of the threads timed out and the other thread
  committed its transaction with that ID, the commit would not become
  visible immediately.  This could lead to deadlock errors in workloads
  that are logically conflict-free.

* Have auto-commit transactions retry deadlocks.  This requires that we
  keep the user's key and value in the cursor.

* Simplify the code handling updated records in variable-length
  column-store reconciliation.

* Never wait for eviction when holding the schema lock.  This avoids
  deadlocks between opening a column store file and taking a checkpoint.

* Take care with the loop termination when walking files for eviction.  We
  were making one extra call into __wt_tree_walk, which would leave a leaf
  page in the WT_REF_EVICT_WALK state, unable to be evicted.  In some
  workloads, including LSM loads, we could end up with many files all
  consisting of a single leaf page, none of which could be evicted.

* Pause updates when the cache is full.

* In files marked as "out of cache", don't wait for eviction when reading a
  page.

* Fix the record count calculation for minor merges.  This was leading to
  no Bloom filter being created for minor merges after running for some
  time, leading to merges taking increasingly long to complete.

* Only sleep in the LSM checkpoint thread if no work is done.

* Add sanity check of cache size to LSM open.

[#338] Create fake checkpoints until an object is modified, so that a
       checkpoint between the cursor create and the bulk load doesn't make
       it impossible to do a bulk-load on the cursor.


WiredTiger release 1.3.1, 2012-09-25
------------------------------------

This is a bugfix release, primarily related to LSM trees.  The changes are
as follows:

[#309] Implement auto-commit of transactions at the API.  As well as
       ensuring the atomicity of complex operations, this change simplified
       code that simulated auto-commit internally and fixed a number of
       bugs.

[#321] Bulk-cursors no longer block checkpoints.  We can't write files that
       are being bulk-loaded, so change checkpoint to create checkpoints in
       the metadata that, if accessed, look like empty files.

       Tighten down the requirements for bulk-load, the only thing that can
       be bulk-loaded now is a newly created tree, not any empty file.

[#329] Add dictionary support to variable-length column store objects.
       Support large row-store reconciliation dictionaries: add a skiplist
       as the indexing mechanism.

[#333] Fix a leak of the in-memory transaction log structure and the LSM
       data source handle.

[#334] Fix a memory leak where a page's replacement address wasn't being
       freed.

* Check that LSM trees are not configured as column stores.

* Fix a race when starting the LSM worker thread. It was possible for the
  thread to exit immediately if it started fast enough.

* Two fixes for LSM, one to ensure that cursors read from a checkpoint if
  one is available. The other to reduce the number of empty chunks that can
  be created initially.

* Fix a bug that disabled bloom filters.

* The configure script checks for Python support in SWIG.

* If a drop operation fails to acquire all of the handle locks it needs,
  make sure it releases the primary handle lock.

* Fix a number of other minor bugs and memory leaks.


WiredTiger release 1.3.0, 2012-09-17
------------------------------------

This release contains a number of major new features, including:

* support for LSM trees with Bloom filters;
* support for hot backups; and
* support for fast truncation of files.

In addition, there are some critical bug fixes.  We recommend that all users
upgrade.  Here is the full list of changes:

[#143] Implement random record lookups.

[#168] Add support for LSM trees.

[#168] Add support for Bloom filters in LSM trees.

[#198] Handle page-generation wraparound.

[#236] Implement hot backups.

[#244] Index cursors for column-store objects may not be created using the
       record number as the index key.

[#247] Add a fast-path for WT_SESSION::truncate that avoids reading most
       data to be deleted.

[#259] Performance hack for cursor open: don't parse the configuration
       strings for a default value if the application didn't specify a
       configuration string.

[#262] Disable dump on child cursors: only the top-level cursor is wrapped
       in a dump cursor.

[#266] Deal with new / dropped indices in __wt_schema_open_index. 

[#269] Checkpoint handles must not be open when they are overwritten. 

[#271] Add support for a reserved checkpoint name "WiredTigerCheckpoint"
       that opens the object's last checkpoint.

[#271] Add the ability to access unnamed checkpoints.

[#274] Change cursor.equals to return a standard error value and store the
       cursor equality result in a separate argument.

[#275] If exclusive handle is required for an operation and it is not
       available, fail immediately: don't block. 

[#276] Fix methods that return integer parameters from Python.  This
       includes cursor.equals and cursor.search_near. 

[#277] Acquire the schema lock when creating the metadata file.  We're
       single-threaded, so it isn't protecting against anything, but the
       handle management code expects to have the schema lock. 

[#279] Some optimizations for __wt_config_gets_defno.  Specifically, if
       we're dealing with a simple stack of config strings, just parse the
       application string rather than the full list of defaults. 

[#279] Split the description string into a set of structures, to reduce the
       number of string comparisons and manipulation that's required.

[#282] Remove the cursor.reconfigure method, and replace it with
       documentation showing how to "reconfigure" cursors using the
       session.open_cursor method to duplicate them with different
       configuration strings.

[#284] Fix for a hazard reference race, where page eviction races with the
       creation of the hazard reference, we have to check the pointer
       itself as well as the state of the pointer.

[#285] We can clear the tree's modified flag on checkpoint, as long as the
       checkpoint writes all modifications.   Clear the tree's modified
       flag before we start the checkpoint, but reset it as necessary if
       reconciliation is unable to write all of the changes in a page.

[#287] Fix __wt_config_check to handle overlapping config values correctly.

[#289] Add support for read-committed isolation, make it the default.  Add
       a session-level "isolation" setting.

[#294] If txn_commit fails, document the transaction was rolled-back.

[#295] Expand the documentation on using cursors without explicit
       transactions. 

[#300] Include all changes whenever closing a file, don't check for
       visibility.  If updates are skipped while evicting a page, give up. 

[#305] Have "wt dump" fail more gracefully if the object doesn't exist.

[#310] When freeing a tracked address in reconcilation, clear it to avoid
       freeing the same address again on error. 

[#314] Replace cursor.equals with cursor.compare

[#319] Clear the bulk_load_ok flag when closing handles. 


* Add an "ancient transaction" statistic so we can find out if they're
  actually occurring in the field.

* Add an "was object ever modified" flag to the btree handle, and use it to
  avoid writing read-only objects during internal checkpoints, issue

* Add per-connection statistics counters for transaction checkpoint, begin,
  commit and rollback.  Add per-btree statistics counters for update
  conflicts.

* Another fixed-length column-store implicit record fix: if the earliest
  row in the object is row 10, and it's on an append list, we still must
  return rows 1-9, they've been implicitly created.

* Bulk cursors: disallow cursor.{equals,next,prev,reset,search,
  search_near,update,remove}; only close and insert are supported.

* Change session.truncate to support any cursor position for range
  truncation, not just keys that are known to exist.

* Checkpoint has to flush the metadata file, but only after it's flushed
  all of the other files.

* Discard obsolete WT_UPDATE structures during updates.

* Document that duplicated cursors are positioned at the same point as the
  cursor that was duplicated.

* Fix a (very unlikely) deadlock at startup, if an application issues a
  checkpoint before the eviction server has managed to open its sesssion.

* Fix a core dump if we verify a file that's corrupted such that we are
  unable to load any checkpoints at all, and the per-checkpoint bit map is
  never set.

* If a page selected for eviction cannot be freed because it has some
  recent updates, try instead to free memory by trimming old updates.

* If a thread fails to evict a page, try to bump its snapshot.  This avoids
  the common case of read-committed threads getting stuck because one
  thread falls behind (e.g., because we can't evict during a checkpoint).

* If an exclusive table create fails, return EEXIST.

* If we try to remove a file that doesn't exist, don't complain, return
  success.

* If we're repeatedly taking a checkpoint with the same name, skip the work
  for read-only objects.

* Instead of flagging the empty tree's leaf page empty as part of creating
  an empty tree in memory, set the page as modified (to force
  reconciliation); if the leaf page is still empty at that time, then we'll
  figure it out during that reconciliation.  This fixes a memory leak where
  the leaf page of a empty tree wasn't being freed.

* It's not unreasonable to open a cursor on a non-existent table, don't
  complain, just return not-found.

* Move dist/RELEASE to the top level of the tree.

* Optimization: don't repeatedly look up btree handles for schema
  operations.

* Return keys from all operations: don't keep pointing to the application's
  key.

* Update btree usage of 64 bitstring implementation, so it's cleaner.

* Update the bitstring implementation to use 64 bit length strings.

* Updates performed without an active transaction should become visible
  with the current transaction ID.

* Upgrade to doxygen 1.8.x

* Use a real snapshot transaction for checkpoints.  Otherwise, the snapshot
  can be updated in between checkpointing multiple files (when updating the
  metadata).


WiredTiger release 1.2.2, 2012-06-20
------------------------------------

This is a bugfix release.  The changes are as follows:

* Defer making free pages available until the end of a checkpoint, in case
  there is a failure after processing some files.

* When checking the value of the "isolation" key, don't assume it is NUL
  terminated.  This bug could cause transactions to run with incorrect
  isolation.

* Fix two bugs with snapshot isolation:

  1. reset the isolation level when the transaction completes;
  2. when checking visibility, check item's ID against the maximum snapshot ID
     (not the transaction's ID).


WiredTiger release 1.2.1, 2012-06-15
------------------------------------

This is a bugfix release.  The changes are as follows:

* Avoid a deadlock between eviction and checkpoint on the connection spinlock.

* Allocate "desc" buffers in heap memory so that they are correctly aligned
  (fixes direct_io support on Linux).

* Initialize the snapshot-avail list after cleaning it out, else we'll try and
  print a NULL pointer in VERBOSE mode.


WiredTiger release 1.2.0, 2012-06-04
------------------------------------

This release contains many bugfixes and improvements.  The major changes are:

[#138]	Add support for transactions with coarse-grained durability.
	Transactions provide atomicity guarantees and rollback, and uncommitted
	changes are never written to disk.  There is no on-disk log, so
	committed changes only become durable when the next checkpoint
	completes.  Checkpoints are implemented by creating
	transactionally-consistent snapshots within data files.

[#156]	Fully support operations that make schema changes with multiple
	sessions open concurrently.

[#159]	Disable internal page key suffix compression if a custom collator is
	configured.  This avoids issues with collators that require complete
	keys.

[#167]	Add support for durable snapshots within files.  While a snapshot is
	active, the pages used by the snapshot will not be overwritten.  If a
	file is accessed after a crash or application exit without calling
	WT_CONNECTION::close, any changes made after the last snapshot will be
	silently ignored.

[#214, #216]
	Fixes for forcing eviction with small caches.

WiredTiger release 1.1.5, 2012-04-26
------------------------------------

Don't update a WT_REF after it has been unlocked.

Add an operation to set a flag atomically, use it to avoid racing on page flags.

Fix a race between sync and reading that could cause a segfault.


WiredTiger release 1.1.4, 2012-04-16
------------------------------------

Check the versions of autoconf, automake and libtool to avoid failures when
trying to build from the github tree with versions that are too old.

[#191] Create the schema table as part of creating the environment so that
       application threads don't race trying to create it later.

[#193] Split-merge pages have to be reconciled to mark their parents dirty

[#194] The dump utility should only output configuration that can be passed to
       WT_SESSION::create.

Eviction fixes for out-of-cache update workloads:

* Fix an unlikely bug where the EVICT_LRU flag was cleared when a page in
  the LRU queue was overwritten with itself during a walk.  This led to an
  assertion failure when the page was later evicted.

* Clear all unused eviction queue entries while holding the lru_lock.

* Split WT_PAGE->flags so that there is no possibility of racing:
  (1) Move WT_PAGE_REC_* flags into WT_PAGE_MODIFY;
  (2) Use atomic operations to set and clear the remaining (2) page flags.

Move the test/format threads setting into the CONFIG file.


WiredTiger release 1.1.3, 2012-04-04
------------------------------------

Fix the "exclusive" config for WT_SESSION::create. [#181]
1. Make it work for files within a single session.
2. Make it work for files across sessions.
3. Make other data sources consistent with files.

Fix an eviction bug introduced into 1.1.2: when evicting a page with children,
remove the children from the LRU eviction queue.  Reduce the impact of clearing
a page from the LRU queue by marking pages on the queue with a flag
(WT_PAGE_EVICT_LRU).  

During an eviction walk, pin pages up to the root so there is no need to spin
when attempting to lock a parent page.  Use the EVICT_LRU page flag to avoid
putting a page on the LRU queue multiple times.

Layer dump cursors on top of any cursor type.

Add a section on replacing the default system memory allocator to the tuning
page.

Typo in usage method for "wt write".

Don't report range errors for config values that aren't well-formed integers.


WiredTiger release 1.1.2, 2012-03-20
------------------------------------

Add public-domain copyright notices to the extension code.

test/format can now run multi-threaded, fixed two bugs it found:
(1) When iterating backwards through a skiplist, we could race with an insert.
(2) If eviction fails for a page, we have to assume that eviction has unlocked
    the reference.

Scan row-store leaf pages twice when reading to reduce the overhead of the
index array.

Eviction race fixes:
(1) Call __rec_review with WT_REFs: don't look at the page until we've checked
    the state.
(2) Clear the eviction point if we hit it when discarding a child page, not
    just the parent.

Eviction tuning changes, particularly for read-only, out-of-cache workloads.

Only notify the eviction server if an application thread doesn't find any pages
to evict, and then only once.

Only spin on the LRU lock if there might be pages in the LRU queue to evict.

Keep the current eviction point in memory and make the eviction walk run
concurrent with LRU eviction.

Every test now has err/out captured, and it is checked to assure it is empty at
the end of every test.


WiredTiger release 1.1.1, 2012-03-12
------------------------------------

Default to a verbose build: that can be switched off by running "configure
--enable-silent-rules").

Account for all memory allocated when reading a page into cache.  Total memory
usage is now much closer to the cache size when using many small keys and
values.

Have application threads trigger a retry forced page eviction rather than
blocking eviction.  This allows rec_evict.c to simply set the WT_REF state to
WT_REF_MEM after all failures, and fixes a bug where pages on the forced
eviction queue would end up with state WT_REF_MEM, meaning they could be chosen
for eviction multiple times.

Grow existing scratch buffers in preference to allocating new ones.

Fix a race between threads reading in and then modifying a page.

Get rid of the pinned flag: it is no longer used.

Fix a race where btree files weren't completely closed before they could be
re-opened.  This behavior can be triggered by using a new session on every
operation (see the new -S flag to the test/thread program).  [#178]

When connections are closed, create a session and discard the btree handles.
This fixes a long-standing bug in closing a connection: if for any reason there
are btree handles still open, we need a real session handle to close them.

Really close btree handles: otherwise we can't safely remove or rename them.
Fixes test failures in test_base02 (among others).

Wait for application threads in LRU eviction to drain before walking a file.

Fix a buffer size calculation when updating the root address of a file.

Documentation fix: 10% of 1MB is 100KB.


WiredTiger release 1.1.0, 2012-02-28
------------------------------------

Add checks to the session.truncate method to ensure the start/stop
cursors reference the same object and have been initialized.

Implement cursor duplication via WT_SESSION::open_cursor.  [#161]

Switch to quiet builds by default.

Fix with automake version < 1.11, use foreign mode so that fewer
top-level files are required.

If a session or connection method is about to return WT_NOTFOUND (some
underlying object was not found), map it to ENOENT, only cursor methods
return WT_NOTFOUND. [#163]

Save and restore session->btree in schema ops to simplify calling code.
[#164]

Note the wiredtiger_open config string "multiprocess" is not yet
supported.

Move "root:F" and "version:F" entries for files into the value for
"file:F", so there is only a single record per file.
[NOTE: SCHEMA CHANGE]

When parsing config strings, continue to the end of the string in case
of repeated keys. [#124]

Don't require shared libraries unless Python is configured.

Add support for direct I/O, with the config "direct_io=(data,log)".
Build with _GNU_SOURCE on Linux to enable O_DIRECT.

Don't keep the last page of column stores pinned: it prevented eviction
of large trees created from scratch.

Allow application threads to evict pages from any tree: maintain a count
of threads doing LRU in each tree and wait for activity to drain when
closing.