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- where 'node' is a constant prefix,
- '00' is node index, it is an incrementing counter of local nodes under same PST root folder,
- remaining is string representation UUID, and this UUID became node's consistent ID.
PST subfolder naming options explained:
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1) A starting node binds to a port and generates old-style compatible consistent ID (e.g. 127.0.0.1:47500) using DiscoverySpi.consistentId(). This method still returns ip:port-based identifier. 2) The node scans the work directory and checks if there is a folder matching the consistent ID. (e.g. work\db\127_0_0_1_49999). If such a folder exists, we start up with this ID (compatibility mode), and we get file lock to this folder. See PdsConsistentIdProcessor.prepareNewSettings. 3) If there are no matching folders, but the directory is not empty, scan it for old-style consistent IDs. If there are old-style db folders, print out a warning (see warning text above), then switch to new style folder generation (step 4). 4) If there are existing new style folders, pick up the one with the smallest sequence number and try to lock the directory. Repeat until we succeed or until the list of new-style consistent IDs is empty. (e.g. work\db\node00-uuid, node01-uuid, etc). 5) If there are no more available new-style folders, generate a new one with next sequence number and random UUID as consistent ID. (e.g. work\db\node00-uuid, uuid overrides uuid in GridDiscoveryManager). 6) Use this consistent ID for the node startup (using value from GridKernalContext.pdsFolderResolver() and from PdsFolderSettings.consistentId()). There is a system property to disable new-style generation and using old-style consistent ID (IgniteSystemProperties.IGNITE_DATA_STORAGE_FOLDER_BY_CONSISTENT_ID). |
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Page store
Ignite Durable Memory is the basis for all data structures. There is no cache state saved on heap now.
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Planned future optimisation - refer data modified from PageDeltaRecord to logical record. Will allow to not store byte updates twice. There is file WAL pointer, pointer to record from the beginning of time. This refreence may be used.
WAL structure
WAL consist of segments (files). The part of segments creates a work directory and files there are cyclically overwritten. Another part is archive - it is sequentially enumerated files, old files are deleted.
WAL file segments and rotation structure is shown at the picture below:
See also WAL history size section below
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There several levels of guarantees (WALMode)
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Implementation | Warranties | |
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| FSYNC | fsync() on each commit | Any crashes (OS and process crash) |
| LOG_ONY | write() on commit Synchronisation is responsibility of OS | Kill process, but no OS fail |
| BACKGROUND | do nothing on commit (records are accumulated in memory) write() on timeout | kill -9 may cause loss of several latest updates |
| NONE | WAL is disabled | data is persisted only in case of graceful cluster shutdown (Ignite.cluster().active(false)) |
But there is several nodes containing same data and there is possible to restore data from other nodes.
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Page size configuration for storage path [/work/db/node00-3a1415b8-aa54-4a63-a40a-c75ad48dd6b8]: 4096; Linux memory page size: 4096; Selected FS block size : 4096.
Selected FS block size : 4096
Direct IO is enabled for block IO operations on aligned memory structures. [block size = 4096, durable memory page size = 4096]
However, disabling plugin’s function is possible through system Property. To disable Direct IO set IgniteSystemProperties#IGNITE_DIRECT_IO_ENABLED to false.
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