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| -rw-r--r-- | Docs/manual.texi | 66 |
1 files changed, 63 insertions, 3 deletions
diff --git a/Docs/manual.texi b/Docs/manual.texi index 69240cf3dc1..62382d89990 100644 --- a/Docs/manual.texi +++ b/Docs/manual.texi @@ -501,6 +501,7 @@ MyISAM Tables * Key space:: Space needed for keys * MyISAM table formats:: MyISAM table formats +* MyISAM table problems:: MyISAM Table Formats @@ -22893,7 +22894,8 @@ based on the @code{ISAM} code and has a lot of useful extensions. The index is stored in a file with the @code{.MYI} (MYIndex) extension, and the data is stored in a file with the @code{.MYD} (MYData) extension. You can check/repair @code{MyISAM} tables with the @code{myisamchk} -utility. @xref{Crash recovery}. +utility. @xref{Crash recovery}. You can compress @code{MyISAM} tables with +@code{myisampack} to take up much less space. @xref{myisampack}. The following is new in @code{MyISAM}: @@ -23046,6 +23048,7 @@ backup media. @menu * Key space:: Space needed for keys * MyISAM table formats:: MyISAM table formats +* MyISAM table problems:: @end menu @cindex key space, MyISAM @@ -23071,7 +23074,7 @@ In @code{MyISAM} tables, you can also prefix compress numbers by specifying many integer keys that have an identical prefix when the numbers are stored high-byte first. -@node MyISAM table formats, , Key space, MyISAM +@node MyISAM table formats, MyISAM table problems, Key space, MyISAM @subsection MyISAM Table Formats @strong{MyISAM} supports 3 different table types. Two of them are chosen @@ -23233,6 +23236,63 @@ columns. Can be uncompressed with @code{myisamchk}. @end itemize +@node MyISAM table problems, , MyISAM table formats, MyISAM +@subsection MyISAM table problems. + +Each @code{MyISAM} @code{.MYI} file has in the header a counter that can +be used to check if a table has been closed properly. + +If you get the following warning from @code{CHECK TABLE} or @code{myisamchk}: + +@example +# clients is using or hasn't closed the table properly +@end example + +this means that this counter has come out of sync. This doesn't mean +that the table is corrupted, but means that you should at least do a +check on the table to verify that it's ok. + +The counter works as follows: + +@itemize @bullet +@item +The first time a table is updated in @strong{MySQL}, a counter in the +header of the index files is incremented. +@item +The counter is not changed during further updates. +@item +When the last instance of a table is closed (because of a @code{FLUSH} or +because there isn't room in the table cache) the counter is +decremented if the table has been updated at any point. +@item +When you repair the table or check the table and it was ok, +the counter is reset to 0. +@item +To avoid problems with interaction with other processes that may do a +check on the table, the counter is not decremented on close if it was 0. +@end itemize + +In other words, the only ways this can go out of sync are: + +@itemize @bullet +@item +The @code{MyISAM} tables are copied without a @code{LOCK} and +@code{FLUSH TABLES}. +@item +@strong{MySQL} has crashed between an update and the final close +(Note that the table may still be ok, as @strong{MySQL} always issues writes +for everything between each statement). +@item +Someone has done a @code{myisamchk --repair} or @code{myisamchk --update-state}on a table that was in use by @code{mysqld}. +@item +Many @code{mysqld} servers are using the table and one has done a +@code{REPAIR} or @code{CHECK} of the table while it was in use by +another server. In this setup the @code{CHECK} is safe to do (even if +you will get the warning from other servers), but @code{REPAIR} should +be avoided as it currently replaces the data file with a new one, which +is not signaled to the other servers. +@end itemize + @cindex tables, merging @cindex MERGE tables, defined @node MERGE, ISAM, MyISAM, Table types @@ -26779,7 +26839,7 @@ tables}. * Replication Options:: Replication Options in my.cnf * Replication SQL:: SQL Commands related to replication * Replication FAQ:: Frequently Asked Questions about replication -* Replication Problems:: Troubleshooting Replication. +* Replication Problems:: Troubleshooting Replication. @end menu @node Replication Intro, Replication Implementation, Replication, Replication |