Version 2.6.1
Upgrading WiredTiger applications

Upgrading to Version 2.6.1

Move the per transaction sync configuration

Move the sync configuration setting from WT_SESSION::begin_transaction to WT_SESSION::commit_transaction. Change the configuration from a boolean to a string with options of on, off, background. Deprecated support for specifying the configuration to WT_SESSION::begin_transaction is maintained for now.

Upgrading to Version 2.6.0

LZ4 compression

The LZ4 compression support has been updated in this release in non-backward compatible ways; tables and files compressed using LZ4 compression with WiredTiger 2.5.3 must be dumped then re-loaded using WiredTiger 2.6.0.

wiredtiger_open file manager configuration changes

The configuration settings related to file handle management have changed significantly in this release. If your application uses the file_manager configuration setting, please refer to the API documentation for the latest settings.

Statistic change

The statistic "log read operations" was removed. The function that used that statistic was never called inside WiredTiger and was also removed.

File handle closing

In WiredTiger, a separate thread of control periodically reviews open objects, closing ones which have been idle for some period of time and discarding them from the cache. In previous WiredTiger releases, this review was independent of the number of open file handles. In this release, WiredTiger only reviews the file handles if at least 250 file handles are open. How often file handles are reviewed (the default is 30 seconds), and how many file handles must be opened before review is triggered, can be configured using the file_manager configuration values to the wiredtiger_open call.

Table drop changes

There has been a functionality change to the WT_SESSION::drop API when the force configuration option is included. The table is now dropped in the background and does not flush data from cache.

Upgrading to Version 2.5.3

Configuration string case-sensitivity

In previous WiredTiger releases, there were several cases where configuration strings were treated in a case-sensitive manner (for example, it was possible to specify "True", "true" or even "tRuE" as a boolean value). For consistency, in this release all WiredTiger configuration strings are case-sensitive, and only "true" will be accepted.

Statistics cursor refresh

In previous releases of WiredTiger, a statistics cursor made a snapshot of the relevant statistics before the first statistics value was read, and those values remained unchanged from that point on, no matter how the cursor was used. In the WiredTiger 2.5.2 release, calling the WT_CURSOR::reset method to reset the cursor refreshes the statistics returned by the cursor.

Buffer alignment on Linux

In previous releases of WiredTiger, all buffers used for I/O were aligned to 4KB boundaries by default. In the WiredTiger 2.5.2 release, alignment is only enforced when direct I/O is configured.

Upgrading to Version 2.5.2

There are no special upgrade steps required.

Upgrading to Version 2.5.1

Statistics cursors on data sources

Opening a statistics cursor on a data source without a checkpoint name no longer aggregates statistics for all open checkpoints on that data source. The returned statistics will only be for the in-memory version of the data source.

For applications that read and write from ordinary tables (without specifying a checkpoint), there will be no change. Applications that opened cursors on checkpoints and relied on their statistics being aggregated into a single statistics cursor will need to open statistics cursors on each checkpoint.

Upgrading to Version 2.5.0


The statistic for the number of bytes written to the log minus the overhead of log record headers and padding was renamed to make the intent clearer. Any applications using the old name will need to be updated.

"none" configuration for collators, compressors and extractors

Collators, compressors and extractors can now be disabled with an explicit "none" value as an alternative to using an empty string. Any applications using the name "none" for a collator, compressor or extractor will need to be updated.

maximum keys and value sizes

The WT_SESSION::create internal_item_max and leaf_item_max configuration strings are now deprecated in favor of the internal_key_max, leaf_key_max, and leaf_value_max configuration strings. See Page and overflow key/value sizes for more information.

Upgrading to Version 2.4.1

The WT_DEADLOCK error return has been deprecated in favor of WT_ROLLBACK to clarify that WT_SESSION::rollback_transaction should be called; no program changes are required.
Statistics keys changed

The names of WiredTiger statistics have been updated to be more consistently named, and simpler to categorize. Any application that was parsing the strings output by statistics will need to be updated.

Upgrading to Version 2.4.0

Default configuration file changes
WiredTiger creates a configuration file when a database is first created. This release adds a version number to that configuration file, and functionality to automatically translate configuration settings between versions moving forward.
Cursors no longer reset on transaction begin or commit

In previous versions of WiredTiger, all cursors in a session were reset at transaction boundaries (WT_SESSION::begin_transaction, WT_SESSION::commit_transaction and WT_SESSION::rollback_transaction). Now they are only reset by WT_SESSION::rollback_transaction.

This change means that a cursor can be used to iterate through a table and perform transactional updates based on the visited records without the cursor losing its position.

Applications relying on this behavior (for example, to avoid pinning the underlying cursor resources), should reset cursors explicitly when the position is no longer required.

WT_COLLATOR interface changes
Add a new WT_COLLATOR::customize callback that WiredTiger will call (if set) for each data source configured to use the collator. Applications using the existing WT_COLLATOR interface that do not require the new functionality should set this callback to NULL.
wiredtiger_open lsm_merge option changed
The global lsm_merge configuration setting has been moved into the lsm_manager option group. To disable merges in all LSM trees pass lsm_manger=(merge=false) to wiredtiger_open.
Java include path search changes
We have updated the configure logic used to search for Java Native Interface files. This fixes problems building WiredTiger's Java API, particularly on OS X, but may introduce problems if your build procedure relied on the old search behavior.
Default mutex implementation changed
The default mutex implementation has been changed from adaptive pthread mutexes to non-adaptive pthread mutexes. Installations can explicitly select adaptive pthread mutexes by specifying –with-spinlock=pthread_adaptive at configuration time.
LSM merge threads option change

The WT_SESSION::create lsm=(merge_threads) configuration option has been replaced by the W::wiredtiger_open lsm_manager=(worker_thread_max) option. The new version specifies a set of LSM threads that are shared across all LSM trees in a database, the older configuration was per LSM table.

Upgrading to Version 2.3.1

wiredtiger_open eviction_workers configuration changed

The eviction_workers configuration setting has been replaced by eviction=(threads_min) and eviction=(threads_max) settings.

There is also a semantic change because eviction_workers used to configure additional threads whereas the new settings configure the total number of threads involved with eviction.

Upgrading to Version 2.3.0

There are no special upgrade steps required.

Upgrading to Version 2.2.1

wiredtiger_open configuration parsing order changed

In the 2.2.1 release, the order that configuration strings are parsed and override earlier values changed. Applications using the Wiredtiger.config file or WIREDTIGER_CONFIG environment variable may need to change. The old order:

  1. default wiredtiger_open configuration
  2. base configuration file, created with the database
  3. user configuration file Wiredtiger.config
  4. user environment variable WIREDTIGER_CONFIG
  5. configuration string passed in to wiredtiger_open

In the new order the user's configuration settings override:

  1. default wiredtiger_open configuration
  2. base configuration file, created with the database
  3. configuration string passed in to wiredtiger_open
  4. user configuration file Wiredtiger.config
  5. user environment variable WIREDTIGER_CONFIG

os_cache_dirty_max off for LSM

In some earlier versions of WiredTiger, creating an LSM table automatically configured os_cache_dirty_max, causing additional system calls that slowed some workloads. Applications that benefit from this setting should set it explicitly in WT_SESSION::create.

transaction_sync setting change

In the 2.2.1 release of WiredTiger the wiredtiger_open transaction_sync configuration setting has changed from a string value to a structure with two fields: method, which corresponds to the previous value (dsync, fsync or none), and enabled, which determines whether there is a sync on every transaction commit by default. Applications can enable or disable sync for a specific transaction with the sync setting to WT_SESSION::begin_transaction.

Upgrading to Version 2.2.0

WT_SESSION::create prefix_compression disabled by default

In the 2.2.0 release, prefix compression default to false. Applications that benefit from prefix compression will need to explicitly set prefix_compression=true when creating tables.

wiredtiger_open verbose message changes

In the 2.2.0 release it is now necessary to include –enable-verbose in the configure command to be able to use verbose messages.

Upgrading to Version 2.1.2

wiredtiger_open shared_cache configuration changes

In the 2.1.2 release of WiredTiger the wiredtiger_open shared_cache configuration option group have changed. The option that was named enable is no longer available. To enable a shared_cache it is compulsory to name the pool being shared. We are now also enforcing that only one of cache_size and shared_cache are specified in the wiredtiger_open configuration string.

Upgrading to Version 2.1.1

WT_EXTENSION_API::config methods

In the 2.1.1 release of WiredTiger the configuration string parsing API has been changed and added to a new public handle. The WT_EXTENSION_API::config_strget, WT_EXTENSION_API::config_scan_begin, WT_EXTENSION_API::config_scan_next and WT_EXTENSION_API::config_scan_end have been removed. They have been replaced by a WT_EXTENSION_API::config_parser_open method, which can be used to parse configuration strings. See the WT_CONFIG_PARSER documentation for examples on how to use the updated API.

Upgrading to Version 2.1

WT_ITEM::size type

In the 2.1 release of WiredTiger WT_ITEM::size type has changed from uint32_t to size_t. Applications may require modifications to resolve compile-time errors.

WT_COMPRESSOR::compress_raw signature

In the 2.1 release of WiredTiger, the behavior of the compress_raw callback has changed so that it will only be retried if it returns EAGAIN. If it returns zero and sets result_slots to zero, WiredTiger will assume that raw compression has failed and will fall back to calling WT_COMPRESSOR::compress.

Transaction sync default setting

In the 2.1 release of WiredTiger the wiredtiger_open transaction_sync configuration setting default value has changed from "dsync" to "fsync". This is due to enhancements to the group commit implementation in WiredTiger - which mean that greater throughput can be achieved with explicit "fsync" calls than by enabling "dsync" on a file handle. Applications that don't execute concurrent transactions may see better throughput with transaction_sync set to "dsync".

Upgrading to Version 2.0

File format changes

The underlying file format is unchanged in 2.0

WT_SESSION::create LSM configuration options

In the 2.0 release of WiredTiger the LSM configuration options have been collected into a configuration option subgroup. All configuration options to WT_SESSION::create that previously had a prefix of lsm_ now belong to the lsm configuration group. If you are explicitly configuring any of the following options, you should review the WT_SESSION::create documentation for details of the updated syntax: lsm_auto_throttle, lsm_bloom, lsm_bloom_config, lsm_bloom_bit_count, lsm_bloom_hash_count, lsm_bloom_oldest, lsm_chunk_max, lsm_chunk_size, lsm_merge_max and lsm_merge_threads.

Upgrading to Version 1.6.6

File format changes

The underlying file formats changed in the 1.6.6 release; tables and files should be dumped and re-loaded into a new database.

WT_SESSION::compact trigger configuration

In previous releases, the trigger configuration string to the WT_SESSION::compact method specified a requirement to initiate compaction; in the 1.6.6 release, this configuration string has been removed, and compaction will be attempted if it seems likely at least 10% of the file can be recovered. Applications may require modifications to resolve run-time errors.

Statistics configuration

In previous releases, the wiredtiger_open function took a statistics configuration, which defaulted to false; when set to true, additional, generally performance-expensive statistics were maintained by the database, above and beyond a default set of statistics. In version 1.6.6, the statistics configuration is a list which may be set to "all", "fast" or "none". When set to "none", no statistics are maintained by the database; when set to "fast", only relatively performance-inexpensive statistics are maintained, and when set to "all", all statistics are maintained, regardless of cost.

In previous releases, the wiredtiger_open function took a statistics_log configuration which logged the performance-inexpensive database statistics to a file. In version 1.6.6, the statistics_log configuration logs whatever statistics are configured for the database. If the database is configured with statistics to "none", no statistics will be logged to the file; if the database is configured with "all" or "fast", the corresponding statistics will be logged to the file.

In previous releases, the WT_SESSION::cursor method took statistics_clear and a statistics_fast configurations. The statistics_clear configuration defaulted to false; when set to true, statistics counters were reset after they were gathered by the cursor. The statistics_fast configuration defaulted to true; when set to true, the cursor only gathered performance-inexpensive statistics for the cursor, and when set to false, the cursor gathered all available statistics, regardless of cost.

In version 1.6.6, these two configuration booleans have been replaced with a new configuration list statistics, which may be set from the values "clear", "fast" and "all". When "fast" is configured, only relatively performance-inexpensive statistics are gathered, and when "all" is configured, all statistics are gathered, regardless of cost. When "clear" is configured, statistics counters are reset after they are gathered.

Additionally, in version 1.6.6, statistics cursors must be configured to agree with the database statistics configuration; when the database statistics are configured to "none", attempts to open a statistics cursor will fail; when the database statistics are configured to "fast", a statistics cursor must also be configured to "fast"; when the database statistics are configured to "all", a statistics cursor may be configured to either "fast" or "all". Opening a statistics cursor without configuring either "fast" or "all" will configure the cursor to be the same as the current database configuration.

Applications may require modifications to resolve run-time errors; application statistics configuration and cursors should be reviewed to confirm they are configured for the desired behavior;

WT_EVENT_HANDLER interface changes

Add a new WT_EVENT_HANDLER::handle_close callback that WiredTiger will call any time it automatically closes an application session or cursor handle.

Additionally add a WT_SESSION parameter into the existing WT_EVENT_HANDLER::handle_error, WT_EVENT_HANDLER::handle_message and WT_EVENT_HANDLER::handle_progress callback functions.

Upgrading to Version 1.6.5

WT_CURSOR::insert behavior

In previous releases, the WT_CURSOR::insert ended positioned at the inserted record. To minimize the cursor resources held by applications inserting many records, the WT_CURSOR::insert method has been changed to end without any position. Application insert cursors should be reviewed to confirm they do not attempt to iterate after an insert.

WT_SESSION::open_cursor statistics_fast configuration

In previous releases, the default statistics_fast configuration to the WT_SESSION::open_cursor method was false; in the 1.6.5 release, the default statistics_fast configuration is true. Applications opening statistics cursors should be reviewed to confirm they have the correct behavior.

Synchronous checkpoint configuration

The sync configuration key to wiredtiger_open has been renamed checkpoint_sync.

Upgrading to Version 1.6.4

File format changes

The underlying file formats changed in the 1.6.4 release; tables and files should be dumped and re-loaded into a new database.

wt utility load command

The default behavior of the wt utility's load command has been changed to overwrite existing data, by default, and the -o flag to the load command (overwrite existing data) has been replaced with the -n flag (do not overwrite existing data). Applications requiring the previous default behavior of not overwriting existing data should add the -n option to their command line configuration; applications previously using the -o option on their command line configurations should remove it.

Upgrading to Version 1.6.3

Cursor overwrite configuration

In previous releases, the WT_SESSION::open_cursor overwrite configuration string behaved inconsistently across Btree and LSM data sources. In Btree, overwrite was false by default and was limited to the WT_CURSOR::insert method, changing an insert to succeed regardless of whether or not the record previously existed. In LSM trees, overwrite was true by default, and applied to the WT_CURSOR::insert, WT_CURSOR::remove and WT_CURSOR::update methods, configuring all three methods to ignore the existing state of the record.

In the 1.6.3 release, the overwrite configuration is consistent across both Btree and LSM tree data sources. For performance reasons, the default is the behavior previously described for LSM trees: in other words, overwrite is true by default, causing WT_CURSOR::insert, WT_CURSOR::remove and WT_CURSOR::update to ignore the current state of the record, and these methods will succeed regardless of whether or not the record previously exists. When an application configures overwrite to false, WT_CURSOR::insert will fail with WT_DUPLICATE_KEY if the record previously exists, and WT_CURSOR::update and WT_CURSOR::remove will fail with WT_NOTFOUND if the record does not previously exist.

This is a potentially serious API change that will not be detected by compilation. Application cursors should be reviewed to confirm they are configured for the desired behavior.

wiredtiger_open no longer accepts a transactional configuration

The transactional configuration key has been removed from wiredtiger_open. Any application setting it should simply remove it, no change in application behavior is needed.

Upgrading to Version 1.6.2

Table of WiredTiger extension methods

New functionality was added to the list of WiredTiger extension methods; applications using the extension methods will require recompilation.

WT_SESSION::create no longer accepts a "source" configuration

The "source" configuration key has been removed from WT_SESSION::create. Normal applications should not have been using it, and there were a number of bugs associated with it.

Default checksum configuration

The default file checksum configuration was changed to uncompressed, which means blocks that are compressed will no longer also include a checksum, by default. Applications using compression insufficient for the purposes of corrupted block identification should change their file checksum configuration to on.

Upgrading to Version 1.6.1

Default page sizes

In the 1.6.1 release, the default for the WT_SESSION::create configuration string allocation_size changed from 512B to 4KB, and the default for the configuration string internal_page_max changed from 2KB to 4KB. Applications wanting to create files with smaller allocation or internal page sizes will need to set those configuration values explicitly.

Shared cache configuration

In the 1.6.1 release, an explicit shared_cache=(enable=boolean) option was added to the wiredtiger_open configuration options. Existing applications that use shared cache functionality will need to add the enable option to the configuration string. The default value for the option is false.

WT_COMPRESSOR::compress_raw signature

In the 1.6.1 release, the split_pct argument to the WT_COMPRESSOR::compress_raw function changed type from u_int to int, applications may require modification to avoid compiler warnings.

Upgrading to Version 1.6.0

File format changes

The underlying file formats changed in the 1.6.0 release; tables and files should be dumped and re-loaded into a new database.

Upgrading to Version 1.5.3

Configuration strings

An undocumented feature where configuration string case was ignored has been removed, and all configuration strings are now case-dependent. Applications may require modifications to resolve run-time errors.

Loading extensions and WT_EXTENSION_API

The following changes are only applicable to applications loading extensions and/or using the WiredTiger extension functions described in WT_EXTENSION_API.

  • The signature of wiredtiger_extension_init has changed from (WT_SESSION *session, WT_EXTENSION_API *api) to (WT_CONNECTION *connection). As no WT_EXTENSION_API handle reference is passed to the function, the WT_CONNECTION::get_extension_api has been added to support retrieval of the extension API. Applications may require modifications.

  • The type of all configuration arguments to extension methods has changed from "const char *" to "WT_CONFIG_ARG *", and the WT_EXTENSION::config method added to support configuration parsing; applications may require modifications.

  • The undocumented wiredtiger_XXX defines for WT_EXTENSION_API extension methods have been removed from the wiredtiger_ext.h include file; applications should instead use the method handles referenced by the WT_EXTENSION_API handle to call extension functions.

  • The extension API methods have all changed to require an additional parameter, the WT_EXTENSION_API method handle; applications may require modifications.

  • The WT_SESSION::msg_printf method was replaced by WT_EXTENSION_API::msg_printf; applications may require modifications.


The following changes are only applicable to applications providing new implementations of the WiredTiger WT_DATA_SOURCE class.

Upgrading to Version 1.4.3


WiredTiger statistics are no longer maintained by default; to configure statistics, use the statistics configuration string to the wiredtiger_open function.

Upgrading to Version 1.3.9


A new member, WT_COMPRESSOR::compress_raw, was added to the WT_COMPRESSOR extension API. Applications using the WT_COMPRESSOR extension API should add a NULL as the second field of that structure.


The WT_SESSION::create method's checksum configuration string has been changed from a boolean type to a string type. Applications using the checksum configuration string should change a value of true to the string on, and a value of false to the string off or the string uncompressed.

File format changes

The underlying file formats changed in the 1.3.9 release; tables and files should be dumped and re-loaded into a new database.

Upgrading to Version 1.3.8

Statistics keys

The statistics key constants have been renamed to use all capitals, and use consistent prefixes to distinguish between connection statistics and statistics for data sources.

Upgrading to Version 1.3.6

Installed library names

The installed WiredTiger extension library names changed to limit namespace pollution:

LibraryPrevious NameNew Name
Bzip2 compressionbzip2_compress.alibwiredtiger_bzip2.a
Snappy compressionsnappy_compress.alibwiredtiger_snappy.a
No-op compressionnop_compress.aNo longer installed
nop_compress.laNo longer installed
nop_compress.soNo longer installed
Reverse order collatorreverse_collator.aNo longer installed
reverse_collator.laNo longer installed
reverse_collator.soNo longer installed

Built-in compression names

The built-in compression name arguments to the WT_SESSION:create block_compressor configuration string changed for consistency:

ExtensionPrevious NameNew Name
Bzip2 compression"bzip2_compress""bzip2"
Snappy compression"snappy_compress""snappy"

Upgrading to Version 1.3.5

File format changes

The underlying file formats changed in the 1.3.5 release; tables and files should be dumped and re-loaded into a new database.

Upgrading to Version 1.3

Checkpoint and Snapshot

The checkpoint functionality supported by WT_SESSION::checkpoint and the snapshot functionality supported by WT_SESSION::sync have been merged into a single piece of functionality.

  • WT_SESSION.checkpoint
    The WT_SESSION::checkpoint method's snapshot configuration string has been renamed to name. The name assigned to checkpoints without a specified name configuration is now "WiredTigerCheckpoint".

  • WT_SESSION.drop
    In releases before 1.3, the WT_SESSION::drop method was used to delete snapshots. In 1.3, the functionality of deleting snapshots has been moved to the WT_SESSION::checkpoint method, specifically, snapshots are discarded using the WT_SESSION::checkpoint method's drop configuration string.

  • WT_SESSION.sync
    The WT_SESSION::sync method has been removed from the 1.3 release; the functionality of creating an object snapshot has moved to the WT_SESSION::checkpoint method, specifically, creating a snapshot of a one or more objects is done using the WT_SESSION::checkpoint method's target configuration string.

  • wt drop -s
    The -s option to the drop command for the wt command line utility has been removed, and object snapshots may no longer be removed from the command line.

  • wt dump, list -s
    The -s options to the dump and list commands for the wt command line utility have been renamed to be -c.


In releases before 1.3, the WT_SESSION::open_cursor method could duplicate cursors that were not positioned in an object; in 1.3, a cursor must be positioned in order to be duplicated.

Transactional cursors

In releases before 1.3, ending a transaction by calling the WT_SESSION::commit_transaction or WT_SESSION::rollback_transaction methods implicitly closed all open cursors; in 1.3, the cursors remain open, but are reset (discarding their positions and cursor values). This means applications must change to either close cursors explicitly, or rely on an eventual WT_SESSION::close or WT_CONNECTION::close methods to implicitly close open cursors.

Default transactional isolation level

In releases before 1.3, the default isolation level for transaction was snapshot, and the default isolation level for non-transaction operations was read-uncommitted; in 1.3, the default isolation level for all operations is read-committed.

The default can be overridden for a session using the isolation setting in WT_CONNECTION::open_cursor.


In releases before 1.3, the WT_SESSION::truncate method required cursors used for truncation of a cursor range to reference existing keys in the object; in 1.3, the WT_SESSION::truncate method has been changed to allow cursors to reference any valid key in the object's name space so applications may discard portions of the object name space without knowing exactly what records the object contains.


In releases before 1.3, the WT_CURSOR::equals method returned zero/non-zero to indicate cursor equality; in 1.3, the WT_CURSOR::equals method has been replaced with WT_CURSOR::compare, which compares two cursors and returns a cursor comparison status (less than 0, equal to 0, or greater than 0) depending on the cursors' key order.

File format changes

The underlying file formats changed in the 1.3 release; tables and files should be dumped and re-loaded into a new database.