VARIABLE_COMMENT Number of pages reserved in doublewrite buffer for batch flushing
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 127
@@ -775,6 +915,20 @@
@@ -789,6 +929,20 @@
ENUM_VALUE_LIST NULL
READ_ONLY YES
COMMAND_LINE_ARGUMENT OPTIONAL
@ -328,7 +328,7 @@
VARIABLE_NAME INNODB_ENCRYPTION_ROTATE_KEY_AGE
SESSION_VALUE NULL
GLOBAL_VALUE 1
@@ -845,13 +999,27 @@
@@ -859,13 +1013,27 @@
ENUM_VALUE_LIST OFF,ON,FORCE
READ_ONLY NO
COMMAND_LINE_ARGUMENT OPTIONAL
@ -357,7 +357,7 @@
VARIABLE_COMMENT Speeds up the shutdown process of the InnoDB storage engine. Possible values are 0, 1 (faster) or 2 (fastest - crash-like).
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 2
@@ -865,7 +1033,7 @@
@@ -879,7 +1047,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 600
VARIABLE_SCOPE GLOBAL
@ -366,7 +366,7 @@
VARIABLE_COMMENT Maximum number of seconds that semaphore times out in InnoDB.
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 4294967295
@@ -935,7 +1103,7 @@
@@ -949,7 +1117,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 0
VARIABLE_SCOPE GLOBAL
@ -375,7 +375,7 @@
VARIABLE_COMMENT Make the first page of the given tablespace dirty.
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 4294967295
@@ -949,7 +1117,7 @@
@@ -963,7 +1131,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 30
VARIABLE_SCOPE GLOBAL
@ -384,7 +384,7 @@
VARIABLE_COMMENT Number of iterations over which the background flushing is averaged.
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 1000
@@ -972,12 +1140,12 @@
@@ -986,12 +1154,12 @@
READ_ONLY NO
COMMAND_LINE_ARGUMENT OPTIONAL
VARIABLE_NAME INNODB_FLUSH_LOG_AT_TRX_COMMIT
@ -400,7 +400,7 @@
VARIABLE_COMMENT Controls the durability/speed trade-off for commits. Set to 0 (write and flush redo log to disk only once per second), 1 (flush to disk at each commit), 2 (write to log at commit but flush to disk only once per second) or 3 (flush to disk at prepare and at commit, slower and usually redundant). 1 and 3 guarantees that after a crash, committed transactions will not be lost and will be consistent with the binlog and other transactional engines. 2 can get inconsistent and lose transactions if there is a power failure or kernel crash but not if mysqld crashes. 0 has no guarantees in case of crash. 0 and 2 can be faster than 1 or 3.
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 3
@@ -1005,7 +1173,7 @@
@@ -1019,7 +1187,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 1
VARIABLE_SCOPE GLOBAL
@ -409,7 +409,7 @@
VARIABLE_COMMENT Set to 0 (don't flush neighbors from buffer pool), 1 (flush contiguous neighbors from buffer pool) or 2 (flush neighbors from buffer pool), when flushing a block
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 2
@@ -1047,7 +1215,7 @@
@@ -1061,7 +1229,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 0
VARIABLE_SCOPE GLOBAL
@ -418,7 +418,7 @@
VARIABLE_COMMENT Helps to save your data in case the disk image of the database becomes corrupt.
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 6
@@ -1055,6 +1223,20 @@
@@ -1069,6 +1237,20 @@
ENUM_VALUE_LIST NULL
READ_ONLY YES
COMMAND_LINE_ARGUMENT REQUIRED
@ -439,7 +439,7 @@
VARIABLE_NAME INNODB_FT_AUX_TABLE
SESSION_VALUE NULL
GLOBAL_VALUE
@@ -1075,7 +1257,7 @@
@@ -1089,7 +1271,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 8000000
VARIABLE_SCOPE GLOBAL
@ -448,7 +448,7 @@
VARIABLE_COMMENT InnoDB Fulltext search cache size in bytes
NUMERIC_MIN_VALUE 1600000
NUMERIC_MAX_VALUE 80000000
@@ -1117,7 +1299,7 @@
@@ -1131,7 +1313,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 84
VARIABLE_SCOPE GLOBAL
@ -457,7 +457,7 @@
VARIABLE_COMMENT InnoDB Fulltext search maximum token size in characters
NUMERIC_MIN_VALUE 10
NUMERIC_MAX_VALUE 84
@@ -1131,7 +1313,7 @@
@@ -1145,7 +1327,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 3
VARIABLE_SCOPE GLOBAL
@ -466,7 +466,7 @@
VARIABLE_COMMENT InnoDB Fulltext search minimum token size in characters
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 16
@@ -1145,7 +1327,7 @@
@@ -1159,7 +1341,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 2000
VARIABLE_SCOPE GLOBAL
@ -475,7 +475,7 @@
VARIABLE_COMMENT InnoDB Fulltext search number of words to optimize for each optimize table call
NUMERIC_MIN_VALUE 1000
NUMERIC_MAX_VALUE 10000
@@ -1159,7 +1341,7 @@
@@ -1173,7 +1355,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 2000000000
VARIABLE_SCOPE GLOBAL
@ -484,7 +484,7 @@
VARIABLE_COMMENT InnoDB Fulltext search query result cache limit in bytes
NUMERIC_MIN_VALUE 1000000
NUMERIC_MAX_VALUE 4294967295
@@ -1187,7 +1369,7 @@
@@ -1201,7 +1383,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 2
VARIABLE_SCOPE GLOBAL
@ -493,7 +493,7 @@
VARIABLE_COMMENT InnoDB Fulltext search parallel sort degree, will round up to nearest power of 2 number
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 16
@@ -1201,7 +1383,7 @@
@@ -1215,7 +1397,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 640000000
VARIABLE_SCOPE GLOBAL
@ -502,7 +502,7 @@
VARIABLE_COMMENT Total memory allocated for InnoDB Fulltext Search cache
NUMERIC_MIN_VALUE 32000000
NUMERIC_MAX_VALUE 1600000000
@@ -1229,7 +1411,7 @@
@@ -1243,7 +1425,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 100
VARIABLE_SCOPE GLOBAL
@ -511,7 +511,7 @@
VARIABLE_COMMENT Up to what percentage of dirty pages should be flushed when innodb finds it has spare resources to do so.
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 100
@@ -1271,10 +1453,10 @@
@@ -1285,10 +1467,10 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 200
VARIABLE_SCOPE GLOBAL
@ -524,7 +524,7 @@
NUMERIC_BLOCK_SIZE 0
ENUM_VALUE_LIST NULL
READ_ONLY NO
@@ -1283,12 +1465,26 @@
@@ -1297,12 +1479,26 @@
SESSION_VALUE NULL
GLOBAL_VALUE 2000
GLOBAL_VALUE_ORIGIN COMPILE-TIME
@ -554,7 +554,7 @@
NUMERIC_BLOCK_SIZE 0
ENUM_VALUE_LIST NULL
READ_ONLY NO
@@ -1321,6 +1517,20 @@
@@ -1335,6 +1531,20 @@
ENUM_VALUE_LIST NULL
READ_ONLY NO
COMMAND_LINE_ARGUMENT REQUIRED
@ -575,7 +575,7 @@
VARIABLE_NAME INNODB_LOCKS_UNSAFE_FOR_BINLOG
SESSION_VALUE NULL
GLOBAL_VALUE OFF
@@ -1355,7 +1565,7 @@
@@ -1369,7 +1579,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 50
VARIABLE_SCOPE SESSION
@ -584,44 +584,26 @@
VARIABLE_COMMENT Timeout in seconds an InnoDB transaction may wait for a lock before being rolled back. Values above 100000000 disable the timeout.
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 1073741824
@@ -1363,37 +1573,107 @@
@@ -1377,16 +1587,72 @@
ENUM_VALUE_LIST NULL
READ_ONLY NO
COMMAND_LINE_ARGUMENT REQUIRED
-VARIABLE_NAME INNODB_LOG_BUFFER_SIZE
-SESSION_VALUE NULL
-GLOBAL_VALUE 1048576
-GLOBAL_VALUE_ORIGIN CONFIG
-DEFAULT_VALUE 16777216
-VARIABLE_SCOPE GLOBAL
-VARIABLE_TYPE BIGINT
-VARIABLE_COMMENT The size of the buffer which InnoDB uses to write log to the log files on disk.
-NUMERIC_MIN_VALUE 262144
-NUMERIC_MAX_VALUE 9223372036854775807
-NUMERIC_BLOCK_SIZE 1024
-ENUM_VALUE_LIST NULL
-READ_ONLY YES
-COMMAND_LINE_ARGUMENT REQUIRED
-VARIABLE_NAME INNODB_LOG_CHECKPOINT_NOW
+VARIABLE_NAME INNODB_LOG_ARCHIVE
SESSION_VALUE NULL
GLOBAL_VALUE OFF
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE OFF
VARIABLE_SCOPE GLOBAL
VARIABLE_TYPE BOOLEAN
-VARIABLE_COMMENT Force checkpoint now
+SESSION_VALUE NULL
+GLOBAL_VALUE OFF
+GLOBAL_VALUE_ORIGIN COMPILE-TIME
+DEFAULT_VALUE OFF
+VARIABLE_SCOPE GLOBAL
+VARIABLE_TYPE BOOLEAN
+VARIABLE_COMMENT Set to 1 if you want to have logs archived.
NUMERIC_MIN_VALUE NULL
NUMERIC_MAX_VALUE NULL
NUMERIC_BLOCK_SIZE NULL
ENUM_VALUE_LIST OFF,ON
READ_ONLY NO
COMMAND_LINE_ARGUMENT OPTIONAL
-VARIABLE_NAME INNODB_LOG_COMPRESSED_PAGES
+NUMERIC_MIN_VALUE NULL
+NUMERIC_MAX_VALUE NULL
+NUMERIC_BLOCK_SIZE NULL
+ENUM_VALUE_LIST OFF,ON
+READ_ONLY NO
+COMMAND_LINE_ARGUMENT OPTIONAL
+VARIABLE_NAME INNODB_LOG_ARCH_DIR
SESSION_VALUE NULL
-GLOBAL_VALUE ON
+SESSION_VALUE NULL
+GLOBAL_VALUE PATH
+GLOBAL_VALUE_ORIGIN COMPILE-TIME
+DEFAULT_VALUE
@ -662,34 +644,25 @@
+ENUM_VALUE_LIST NULL
+READ_ONLY YES
+COMMAND_LINE_ARGUMENT REQUIRED
+VARIABLE_NAME INNODB_LOG_BUFFER_SIZE
+SESSION_VALUE NULL
+GLOBAL_VALUE 1048576
+GLOBAL_VALUE_ORIGIN CONFIG
+DEFAULT_VALUE 16777216
+VARIABLE_SCOPE GLOBAL
VARIABLE_NAME INNODB_LOG_BUFFER_SIZE
SESSION_VALUE NULL
GLOBAL_VALUE 1048576
GLOBAL_VALUE_ORIGIN CONFIG
DEFAULT_VALUE 16777216
VARIABLE_SCOPE GLOBAL
-VARIABLE_TYPE BIGINT
+VARIABLE_TYPE INT
+VARIABLE_COMMENT The size of the buffer which InnoDB uses to write log to the log files on disk.
+NUMERIC_MIN_VALUE 262144
VARIABLE_COMMENT The size of the buffer which InnoDB uses to write log to the log files on disk.
VARIABLE_COMMENT Number of log files in the log group. InnoDB writes to the files in a circular fashion.
NUMERIC_MIN_VALUE 2
NUMERIC_MAX_VALUE 100
@@ -1453,9 +1733,37 @@
@@ -1467,9 +1747,37 @@
GLOBAL_VALUE_ORIGIN CONFIG
DEFAULT_VALUE 1024
VARIABLE_SCOPE GLOBAL
@ -758,7 +728,7 @@
NUMERIC_MAX_VALUE 18446744073709551615
NUMERIC_BLOCK_SIZE 0
ENUM_VALUE_LIST NULL
@@ -1495,10 +1803,10 @@
@@ -1509,10 +1817,10 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 0
VARIABLE_SCOPE GLOBAL
@ -771,7 +741,7 @@
NUMERIC_BLOCK_SIZE 0
ENUM_VALUE_LIST NULL
READ_ONLY NO
@@ -1509,7 +1817,7 @@
@@ -1523,7 +1831,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 0
VARIABLE_SCOPE GLOBAL
@ -780,7 +750,7 @@
VARIABLE_COMMENT Maximum delay of user threads in micro-seconds
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 10000000
@@ -1523,7 +1831,7 @@
@@ -1537,7 +1845,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 0
VARIABLE_SCOPE GLOBAL
@ -789,7 +759,7 @@
VARIABLE_COMMENT Number of identical copies of log groups we keep for the database. Currently this should be set to 1.
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 10
@@ -1593,7 +1901,7 @@
@@ -1607,7 +1915,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 8
VARIABLE_SCOPE GLOBAL
@ -798,7 +768,12 @@
VARIABLE_COMMENT Number of multi-threaded flush threads
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 64
@@ -1649,10 +1957,10 @@
@@ -1659,14 +1967,14 @@
COMMAND_LINE_ARGUMENT REQUIRED
VARIABLE_NAME INNODB_OPEN_FILES
SESSION_VALUE NULL
-GLOBAL_VALUE 2000
+GLOBAL_VALUE 300
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 0
VARIABLE_SCOPE GLOBAL
@ -811,7 +786,7 @@
NUMERIC_BLOCK_SIZE 0
ENUM_VALUE_LIST NULL
READ_ONLY YES
@@ -1677,7 +1985,7 @@
@@ -1691,7 +1999,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 16
VARIABLE_SCOPE GLOBAL
@ -820,7 +795,7 @@
VARIABLE_COMMENT Number of rw_locks protecting buffer pool page_hash. Rounded up to the next power of 2
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 1024
@@ -1691,7 +1999,7 @@
@@ -1705,7 +2013,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 16384
VARIABLE_SCOPE GLOBAL
@ -829,7 +804,7 @@
VARIABLE_COMMENT Page size to use for all InnoDB tablespaces.
NUMERIC_MIN_VALUE 4096
NUMERIC_MAX_VALUE 65536
@@ -1727,13 +2035,83 @@
@@ -1741,13 +2049,83 @@
ENUM_VALUE_LIST OFF,ON
READ_ONLY NO
COMMAND_LINE_ARGUMENT OPTIONAL
@ -914,7 +889,7 @@
VARIABLE_COMMENT Number of UNDO log pages to purge in one batch from the history list.
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 5000
@@ -1775,7 +2139,7 @@
@@ -1789,7 +2167,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 1
VARIABLE_SCOPE GLOBAL
@ -923,7 +898,7 @@
VARIABLE_COMMENT Purge threads can be from 1 to 32. Default is 1.
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 32
@@ -1803,7 +2167,7 @@
@@ -1817,7 +2195,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 56
VARIABLE_SCOPE GLOBAL
@ -932,7 +907,7 @@
VARIABLE_COMMENT Number of pages that must be accessed sequentially for InnoDB to trigger a readahead.
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 64
@@ -1817,7 +2181,7 @@
@@ -1831,7 +2209,7 @@
GLOBAL_VALUE_ORIGIN CONFIG
DEFAULT_VALUE 4
VARIABLE_SCOPE GLOBAL
@ -941,7 +916,7 @@
VARIABLE_COMMENT Number of background read I/O threads in InnoDB.
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 64
@@ -1845,10 +2209,10 @@
@@ -1859,10 +2237,10 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 0
VARIABLE_SCOPE GLOBAL
@ -954,7 +929,7 @@
NUMERIC_BLOCK_SIZE 0
ENUM_VALUE_LIST NULL
READ_ONLY NO
@@ -1873,7 +2237,7 @@
@@ -1887,7 +2265,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 128
VARIABLE_SCOPE GLOBAL
@ -963,7 +938,7 @@
VARIABLE_COMMENT Number of undo logs to use (deprecated).
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 128
@@ -1887,7 +2251,7 @@
@@ -1901,7 +2279,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 0
VARIABLE_SCOPE GLOBAL
@ -972,7 +947,7 @@
VARIABLE_COMMENT An InnoDB page number.
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 4294967295
@@ -1895,6 +2259,48 @@
@@ -1909,6 +2287,48 @@
ENUM_VALUE_LIST NULL
READ_ONLY NO
COMMAND_LINE_ARGUMENT OPTIONAL
@ -1021,7 +996,7 @@
VARIABLE_NAME INNODB_SCRUB_LOG
SESSION_VALUE NULL
GLOBAL_VALUE OFF
@@ -1923,6 +2329,34 @@
@@ -1937,6 +2357,34 @@
ENUM_VALUE_LIST NULL
READ_ONLY NO
COMMAND_LINE_ARGUMENT OPTIONAL
@ -1056,7 +1031,7 @@
VARIABLE_NAME INNODB_SIMULATE_COMP_FAILURES
SESSION_VALUE NULL
GLOBAL_VALUE 0
@@ -1943,7 +2377,7 @@
@@ -1957,7 +2405,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 1048576
VARIABLE_SCOPE GLOBAL
@ -1065,7 +1040,7 @@
VARIABLE_COMMENT Memory buffer size for index creation
NUMERIC_MIN_VALUE 65536
NUMERIC_MAX_VALUE 67108864
@@ -1957,10 +2391,10 @@
@@ -1971,10 +2419,10 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 6
VARIABLE_SCOPE GLOBAL
@ -1078,7 +1053,7 @@
NUMERIC_BLOCK_SIZE 0
ENUM_VALUE_LIST NULL
READ_ONLY NO
@@ -2000,7 +2434,7 @@
@@ -2014,7 +2462,7 @@
DEFAULT_VALUE nulls_equal
VARIABLE_SCOPE GLOBAL
VARIABLE_TYPE ENUM
@ -1087,7 +1062,7 @@
NUMERIC_MIN_VALUE NULL
NUMERIC_MAX_VALUE NULL
NUMERIC_BLOCK_SIZE NULL
@@ -2167,7 +2601,7 @@
@@ -2181,7 +2629,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 1
VARIABLE_SCOPE GLOBAL
@ -1096,7 +1071,7 @@
VARIABLE_COMMENT Size of the mutex/lock wait array.
NUMERIC_MIN_VALUE 1
NUMERIC_MAX_VALUE 1024
@@ -2181,10 +2615,10 @@
@@ -2195,10 +2643,10 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 30
VARIABLE_SCOPE GLOBAL
@ -1109,7 +1084,7 @@
NUMERIC_BLOCK_SIZE 0
ENUM_VALUE_LIST NULL
READ_ONLY NO
@@ -2209,7 +2643,7 @@
@@ -2223,7 +2671,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 0
VARIABLE_SCOPE GLOBAL
@ -1118,7 +1093,7 @@
VARIABLE_COMMENT Helps in performance tuning in heavily concurrent environments. Sets the maximum number of threads allowed inside InnoDB. Value 0 will disable the thread throttling.
NUMERIC_MIN_VALUE 0
NUMERIC_MAX_VALUE 1000
@@ -2223,7 +2657,7 @@
@@ -2237,7 +2685,7 @@
GLOBAL_VALUE_ORIGIN COMPILE-TIME
DEFAULT_VALUE 10000
VARIABLE_SCOPE GLOBAL
@ -1127,7 +1102,7 @@
VARIABLE_COMMENT Time of innodb thread sleeping before joining InnoDB queue (usec). Value 0 disable a sleep
VARIABLE_COMMENT Controls the durability/speed trade-off for commits. Set to 0 (write and flush redo log to disk only once per second), 1 (flush to disk at each commit), 2 (write to log at commit but flush to disk only once per second) or 3 (flush to disk at prepare and at commit, slower and usually redundant). 1 and 3 guarantees that after a crash, committed transactions will not be lost and will be consistent with the binlog and other transactional engines. 2 can get inconsistent and lose transactions if there is a power failure or kernel crash but not if mysqld crashes. 0 has no guarantees in case of crash. 0 and 2 can be faster than 1 or 3.