xSQL Database Parameters

The xSQL configuration file can be used to define database parameters corresponding to the C API mco_db_params_t structure.

For an overview see page Configuration File Parameters

The db_params section consists of a set of "name : value" pairs enclosed within braces. For example: 

 
    db_params : {
        mem_page_size : 256,
        disk_page_size : 4096,
        db_max_connections : 100,
        ...
    }
     

The following table lists the possible options for the db_params section with the corresponding C API structures and values specified in the comment:

Option name : example value Comment
mem_page_size : 256, In-memory page size (mco_db_params_t::mem_page_size), unsigned.
disk_page_size : 4096, Disk page size (mco_db_params_t::disk_page_size), unsigned
db_max_connections : 100, Max number of connections (mco_db_params_t::db_max_connections), unsigned
disk_max_database_size : 0, Max size of persistent database (mco_db_params_t::disk_max_database_size), unsigned
file_extension_quantum : 0, Quantum of increase in the size of the database file (mco_db_params_t::file_extension_quantum), unsigned
db_log_type : redo,

Database logging method (mco_db_params_t::db_log_type), one of

no (NO_LOG),

redo (REDO_LOG) or

undo (UNDO_LOG)

aio_queue_length : 20000, Asynchronous I/O queue length (default is 10007)
additional_heap_size : 3m, Additional heap memory (this can be necessary when altering or dropping tables)
hash_load_factor : 100, Criteria of hash reallocation in percent of used items (mco_db_params_t::hash_load_factor), unsigned
index_optimistic_lock_threshold : 100, Maximum number of active write transactions when optimistic locking of B-Tree indexes can be performed
log_params: {...} Log settings (mco_db_params_t::log_params) (See below Log Params )
mode_mask : [],

Open mode mask (mco_db_params_t::mode_mask), combination of

mvcc_auto_vacuum (MCO_DB_MODE_MVCC_AUTO_VACUUM),

smart_index_insert (MCO_DB_MODE_SMART_INDEX_INSERT),

open_existing (MCO_DB_OPEN_EXISTING),

use_crc_check (MCO_DB_USE_CRC_CHECK),

transient (MCO_DB_TRANSIENT),

lazy_mem_initialization (MCO_DB_LAZY_MEM_INITIALIZATION),

mursiw_disk_commit_optimization (MCO_DB_MURSIW_DISK_COMMIT_OPTIMIZATION),

bulk_write_modified_pages (MCO_DB_BULK_WRITE_MODIFIED_PAGES),

index_preload (MCO_DB_INDEX_PRELOAD) ,

disable_nested_transactions (MCO_DB_DISABLE_NESTED_TRANSACTIONS),

disable_implicit_rollback (MCO_DB_DISABLE_IMPLICIT_ROLLBACK),

inmemory_protection (MCO_DB_INMEMORY_PROTECTION),

inmemory_compression (MCO_DB_INMEMORY_COMPRESSION),

inclusive_btree (MCO_DB_INCLUSIVE_BTREE) ,

separate_bitmap (MCO_DB_SEPARATE_BITMAP) ,

disable_btree_rebalance_on_delete (MCO_DB_DISABLE_BTREE_REBALANCE_ON_DELETE),

auto_rollback_first_phase (MCO_DB_AUTO_ROLLBACK_FIRST_PHASE),

mvcc_compatibility_mode (MCO_DB_MVCC_COMPATIBILITY_MODE),

disable_page_pool_reserve (MCO_DB_DISABLE_PAGE_POOL_RESERVE),

redo_log_optimization (MCO_DB_REDO_LOG_OPTIMIZATION),

disable_hot_updates (MCO_DB_DISABLE_HOT_UPDATES),

sql_autocheckpoint (MCO_DB_SQL_AUTOCHECKPOINT),

read_only (MCO_DB_MODE_READ_ONLY),

use_aio (MCO_DB_USE_AIO),

incremental_backup (MCO_DB_INCREMENTAL_BACKUP),

mvcc_table_level_locking (MCO_DB_MVCC_TABLE_LEVEL_LOCKING)

min_conn_local_pages : 256, Minimum number of pages in per-connection allocator (mco_db_params_t::min_conn_local_pages), unsigned
max_conn_local_pages : 1024, Maximum number of pages in per-connection allocator (mco_db_params_t::max_conn_local_pages), unsigned
allocation_bitmap_caching_priority : 0, Priority of allocator bitmap pages in LRU page pool (mco_db_params_t::allocation_bitmap_caching_priority), integer
index_caching_priority : 0, Priority of index pages in LRU page pool (mco_db_params_t::index_caching_priority), integer
object_caching_priority : 0, Priority of object (non-blob) pages in LRU page pool (mco_db_params_t::object_caching_priority), integer
cipher_key : "secret", Database encryption key (mco_db_params_t::cipher_key), string (see page Encryption and Compression for details.)
dynamic_hash : true, Dynamically extend hash table when number of items exceeds load factor (mco_db_params_t::dynamic_hash), boolean
license_key : "ABCABCABCABC", # eXtremeDB license key (mco_db_params_t::license_key) ,string
ddl_dict_size :64K, # Used to reserve space for the dictionary in the database header to allow dynamic table creation (mco_db_params_t::ddl_dict_size), unsigned
max_classes : 100, Used to reserve space for classes in the database header to allow dynamic table creation (mco_db_params_t::max_classes), unsigned
max_indexes : 100, Used to reserve space for indexes in the database header to allow dynamic table creation (mco_db_params_t::max_indexes), unsigned
autocompact_threshold : 100k, Size of object after reaching which mco_w_compact() is called during transaction commit (mco_db_params_t::autocompact_threshold), unsigned
trans_sched_policy : fifo

Scheduling policy for transactions with the same priority (mco_db_params_t::trans_sched_policy). One of

fifo (MCO_SCHED_FIFO),

reader_favor (MCO_SCHED_READER_FAVOR) or

writer_favor (MCO_SCHED_WRITER_FAVOR)
max_active_pages: 32, Maximum number of pages accessed by connection (mco_db_params_t::max_active_pages), unsigned
page_hash_bundles: 8, Number of bundles in encryption / protection / compression page hash (mco_db_params_t::page_hash_bundles), unsigned
compression_level: 0, Compression level (mco_db_params_t::compression_level), 0..9, 0 = no compression
compression_mask: 0x1, Bitmap of page kinds which should be compressed, (mco_db_params_t::compression_mask), unsigned
expected_compression_ratio: 10, Used to allocate page map: virtual database space can not be larger than physical size * compression ratio, (mco_db_params_t::expected_compression_ratio), unsigned
btree_cursor_read_ahead_size : 3, Number of keys taken from a leaf B-Tree page at each access, cannot be larger than MCO_CFG_CURSOR_BUF_SIZE, (mco_db_params_t::btree_cursor_read_ahead_size), unsigned
mvcc_bitmap_size MVCC bitmap size (should be power of two)
additional_heap_size Heap memory used by various internal DB functionalities, mostly for buffering during heap memory used by various internal DB functionalities
cow_pagemap_size Size of copy-on-write MVCC pagemap (in bytes, one byte per disk page)
backup_map_size Size of backup counters array, bytes, power of two, ignored if disk_max_database_size set to zero to disable backup feature
backup_min_pages Number of pages for last exclusive pass of backup procedure (set to zero to disable threshold)
backup_max_passes Max number of passes before exclusive pass of backup procedure
backup_map_filename

Name of a file will be used to store backup temporary data on mco_db_close() call eXtremeDB will use file system wrapper linked into the process to store the data optional (set zero for default "<persistent-storage>.bmap" file located at the same location as persistent storage file)
iot_agent_id The IoT agent Identifier
file_backup_delay The delay in milliseconds between writing backup blocks; to minimize backup impact on performance; default is 0 - no delay. (See File Backup)

Log Params

The following table lists the possible options for the log_params section with the corresponding C API structures and values specified in the comment:

Option name : example value Comment
default_commit_policy : buffered,

Transaction commit policy (mco_log_params_t::default_commit_policy), one of :

  • sync_flush (MCO_COMMIT_SYNC_FLUSH),
  • buffered (MCO_COMMIT_BUFFERED),
  • delayed (MCO_COMMIT_DELAYED) or
  • no_sync (MCO_COMMIT_NO_SYNC)
redo_log_limit : 16m, Redo log file size limit (mco_log_params_t::redo_log_limit), unsigned
delayed_commit_threshold : 0, Delayed commit threshold (mco_log_params_t::delayed_commit_threshold), unsigned
max_delayed_transactions : 100, Delayed commit transactions (mco_log_params_t::max_delayed_transactions), unsigned
max_commit_delay : 1000 Delay for commit (mco_log_params_t::max_commit_delay), unsigned
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