Commit graph

2007 commits

Author SHA1 Message Date
Sergei Golubchik
f486f49e8d MDEV-4824 userstats - wrong user statistics
(and valgrind warnings)

* move thd userstat initialization to the same function
  that was adding thd userstat to global counters.
* initialize thd->start_bytes_received in THD::init
  (when thd->userstat_running is set)
2013-11-11 16:17:32 +01:00
unknown
57a267a8c0 Merge from 10.0-base to 10.0 the feature MDEV-4506: Parallel replication.
The merge is still missing a few hunks related to temporary tables and
InnoDB log file size. The associated code did not seem to exist in
10.0, so the merge of that needs more work. Until this is fixed, there
are a number of test failures as a result.
2013-11-01 12:00:11 +01:00
unknown
cb86ce60b9 Merge MDEV-4506: Parallel replication into 10.0-base. 2013-11-01 09:17:06 +01:00
Sergei Golubchik
0fdb3bcfdb 10.0-base merge (roles) 2013-10-29 15:08:44 +01:00
Sergei Golubchik
b2f16628cf support DEFINER=role and DEFINER=current_role 2013-10-18 12:17:49 -07:00
Vicențiu Ciorbaru
7ec24435b3 Added acl_setrole function. The function enables/disables role privileges to
the current user via the current security_context
2013-10-17 15:11:13 -07:00
Sergey Petrunya
1e36cbfa39 MDEV-3798: [SHOW] EXPLAIN UPDATE/DELETE
- Merge with 10.0-base
2013-10-15 11:51:41 +04:00
Sergey Petrunya
a06170c8d8 MDEV-3798: EXPLAIN UPDATE/DELETE
- Fix a problem with EXPLAIN multi_table UPDATE: 
  = Do use multi_update object, because multi_update::prepare() does
    various setup, e.g. it disables index-only for the tables to be updated.
  = Protect multi_update::prepare() from being invoked multiple times. 
    If the query has subqueries, they may try to invoke it, for some reason.
2013-10-15 10:34:46 +04:00
unknown
2842f6b5dc MDEV-4506: Parallel replication: error handling.
Add an error code to the wait_for_commit facility.

Now, when a transaction fails, it can signal the error to
any subsequent transaction that is waiting for it to commit.
The waiting transactions then receive the error code back from
wait_for_prior_commit() and can handle the error appropriately.

Also fix one race that could cause crash if @@slave_parallel_threads
were changed several times quickly in succession.
2013-10-14 15:28:16 +02:00
Michael Widenius
2e100cc5a4 Fixes for parallel slave:
- Made slaves temporary table multi-thread slave safe by adding mutex around save_temporary_table usage.
  - rli->save_temporary_tables is the active list of all used temporary tables
  - This is copied to THD->temporary_tables when temporary tables are opened and updated when temporary tables are closed
  - Added THD->lock_temporary_tables() and THD->unlock_temporary_tables() to simplify this.
- Relay_log_info->sql_thd renamed to Relay_log_info->sql_driver_thd to avoid wrong usage for merged code.
- Added is_part_of_group() to mark functions that are part of the next function. This replaces setting IN_STMT when events are executed.
- Added is_begin(), is_commit() and is_rollback() functions to Query_log_event to simplify code.
- If slave_skip_counter is set run things in single threaded mode. This simplifies code for skipping events.
- Updating state of relay log (IN_STMT and IN_TRANSACTION) is moved to one single function: update_state_of_relay_log()
  We can't use OPTION_BEGIN to check for the state anymore as the sql_driver and sql execution threads may be different.
  Clear IN_STMT and IN_TRANSACTION in init_relay_log_pos() and Relay_log_info::cleanup_context() to ensure the flags doesn't survive slave restarts
  is_in_group() is now independent of state of executed transaction.
- Reset thd->transaction.all.modified_non_trans_table() if we did set it for single table row events.
  This was mainly for keeping the flag as documented.
- Changed slave_open_temp_tables to uint32 to be able to use atomic operators on it.
- Relay_log_info::sleep_lock -> rpl_group_info::sleep_lock
- Relay_log_info::sleep_cond -> rpl_group_info::sleep_cond
- Changed some functions to take rpl_group_info instead of Relay_log_info to make them multi-slave safe and to simplify usage
  - do_shall_skip()
  - continue_group()
  - sql_slave_killed()
  - next_event()
- Simplifed arguments to io_salve_killed(), check_io_slave_killed() and sql_slave_killed(); No reason to supply THD as this is part of the given structure.
- set_thd_in_use_temporary_tables() removed as in_use is set on usage
- Added information to thd_proc_info() which thread is waiting for slave mutex to exit.
- In open_table() reuse code from find_temporary_table()

Other things:
- More DBUG statements
- Fixed the rpl_incident.test can be run with --debug
- More comments
- Disabled not used function rpl_connect_master()

mysql-test/suite/perfschema/r/all_instances.result:
  Moved sleep_lock and sleep_cond to rpl_group_info
mysql-test/suite/rpl/r/rpl_incident.result:
  Updated result
mysql-test/suite/rpl/t/rpl_incident-master.opt:
  Not needed anymore
mysql-test/suite/rpl/t/rpl_incident.test:
  Fixed that test can be run with --debug
sql/handler.cc:
  More DBUG_PRINT
sql/log.cc:
  More comments
sql/log_event.cc:
  Added DBUG statements
  do_shall_skip(), continue_group() now takes rpl_group_info param
  Use is_begin(), is_commit() and is_rollback() functions instead of inspecting query string
  We don't have set slaves temporary tables 'in_use' as this is now done when tables are opened.
  Removed IN_STMT flag setting. This is now done in update_state_of_relay_log()
  Use IN_TRANSACTION flag to test state of relay log.
  In rows_event_stmt_cleanup() reset thd->transaction.all.modified_non_trans_table if we had set this before.
sql/log_event.h:
  do_shall_skip(), continue_group() now takes rpl_group_info param
  Added is_part_of_group() to mark events that are part of the next event. This replaces setting IN_STMT when events are executed.
  Added is_begin(), is_commit() and is_rollback() functions to Query_log_event to simplify code.
sql/log_event_old.cc:
  Removed IN_STMT flag setting. This is now done in update_state_of_relay_log()
  do_shall_skip(), continue_group() now takes rpl_group_info param
sql/log_event_old.h:
  Added is_part_of_group() to mark events that are part of the next event.
  do_shall_skip(), continue_group() now takes rpl_group_info param
sql/mysqld.cc:
  Changed slave_open_temp_tables to uint32 to be able to use atomic operators on it.
  Relay_log_info::sleep_lock -> Rpl_group_info::sleep_lock
  Relay_log_info::sleep_cond -> Rpl_group_info::sleep_cond
sql/mysqld.h:
  Updated types and names
sql/rpl_gtid.cc:
  More DBUG
sql/rpl_parallel.cc:
  Updated TODO section
  Set thd for event that is execution
  Use new  is_begin(), is_commit() and is_rollback() functions.
  More comments
sql/rpl_rli.cc:
  sql_thd -> sql_driver_thd
  Relay_log_info::sleep_lock -> rpl_group_info::sleep_lock
  Relay_log_info::sleep_cond -> rpl_group_info::sleep_cond
  Clear IN_STMT and IN_TRANSACTION in init_relay_log_pos() and Relay_log_info::cleanup_context() to ensure the flags doesn't survive slave restarts.
  Reset table->in_use for temporary tables as the table may have been used by another THD.
  Use IN_TRANSACTION instead of OPTION_BEGIN to check state of relay log.
  Removed IN_STMT flag setting. This is now done in update_state_of_relay_log()
sql/rpl_rli.h:
  Changed relay log state flags to bit masks instead of bit positions (most other code we have uses bit masks)
  Added IN_TRANSACTION to mark if we are in a BEGIN ... COMMIT section.
  save_temporary_tables is now thread safe
  Relay_log_info::sleep_lock -> rpl_group_info::sleep_lock
  Relay_log_info::sleep_cond -> rpl_group_info::sleep_cond
  Relay_log_info->sql_thd renamed to Relay_log_info->sql_driver_thd to avoid wrong usage for merged code
  is_in_group() is now independent of state of executed transaction.
sql/slave.cc:
  Simplifed arguments to io_salve_killed(), sql_slave_killed() and check_io_slave_killed(); No reason to supply THD as this is part of the given structure.
  set_thd_in_use_temporary_tables() removed as in_use is set on usage in sql_base.cc
  sql_thd -> sql_driver_thd
  More DBUG
  Added update_state_of_relay_log() which will calculate the IN_STMT and IN_TRANSACTION state of the relay log after the current element is executed.
  If slave_skip_counter is set run things in single threaded mode.
  Simplifed arguments to io_salve_killed(), check_io_slave_killed() and sql_slave_killed(); No reason to supply THD as this is part of the given structure.
  Added information to thd_proc_info() which thread is waiting for slave mutex to exit.
  Disabled not used function rpl_connect_master()
  Updated argument to next_event()
sql/sql_base.cc:
  Added mutex around usage of slave's temporary tables. The active list is always kept up to date in sql->rgi_slave->save_temporary_tables.
  Clear thd->temporary_tables after query (safety)
  More DBUG
  When using temporary table, set table->in_use to current thd as the THD may be different for slave threads.
  Some code is ifdef:ed with REMOVE_AFTER_MERGE_WITH_10 as the given code in 10.0 is not yet in this tree.
  In open_table() reuse code from find_temporary_table()
sql/sql_binlog.cc:
  rli->sql_thd -> rli->sql_driver_thd
  Remove duplicate setting of rgi->rli
sql/sql_class.cc:
  Added helper functions rgi_lock_temporary_tables() and rgi_unlock_temporary_tables()
  Would have been nicer to have these inline, but there was no easy way to do that
sql/sql_class.h:
  Added functions to protect slaves temporary tables
sql/sql_parse.cc:
  Added DBUG_PRINT
sql/transaction.cc:
  Added comment
2013-10-14 00:24:05 +03:00
Sergey Petrunya
e5d13c1567 Merge 10.0-base -> 10.0 2013-10-16 13:38:42 +04:00
Alexander Barkov
0b6c4bb34f MDEV-4928 Merge collation customization improvements
Merging the following MySQL-5.6 changes:
- WL#5624: Collation customization improvements
  http://dev.mysql.com/worklog/task/?id=5624

- WL#4013: Unicode german2 collation
  http://dev.mysql.com/worklog/task/?id=4013

- Bug#62429 XML: ExtractValue, UpdateXML max arg length 127 chars
  http://bugs.mysql.com/bug.php?id=62429
  (required by WL#5624)
2013-10-02 15:04:07 +04:00
Sergei Golubchik
9af177042e 10.0-base merge.
Partitioning/InnoDB changes are *not* merged (they'll come from 5.6)
TokuDB does not compile (not updated to 10.0 SE API)
2013-09-21 10:14:42 +02:00
Sergey Petrunya
2add402891 MDEV-407: Print EXPLAIN [ANALYZE] in the slow query log
- Initial implementation.
2013-09-19 08:33:58 +04:00
Sergei Golubchik
4ec2e9d7ed 5.5 merge and fixes for compiler/test errors 2013-09-18 13:07:31 +02:00
Sergey Vojtovich
1a2a9d74fe MDEV-4911 - add KILL query id, and add query id information to processlist
It is now possible to kill query by query id. KILL syntax was extended to:
KILL [HARD | SOFT] [CONNECTION | QUERY [ID query_id]] [thread_id | USER user_name]

Added QUERY_ID column to INFORMATION_SCHEMA.PROCESSLIST.

Fixed tests affected by this change:
- added PROCESSLIST.QUERY_ID column
- ID is now keyword and is quoted in SHOW CREATE TABLE output
- PFS statement digest is calculated basing on token id
  (not token text). Token id has shifted for keywords residing
  after ID in keywords array.
2013-09-13 20:14:56 +04:00
unknown
d107bdaa01 MDEV-4506, parallel replication.
Some after-review fixes.
2013-09-13 15:09:57 +02:00
Sergey Vojtovich
bbc9e57981 MDEV-4978 - Server cursor is broken with blobs in the select list,
ORDER BY does not work

Use "dynamic" row format (instead of "block") for MARIA internal
temporary tables created for cursors.

With "block" row format MARIA may shuffle rows, with "dynamic" row
format records are inserted sequentially (there are no gaps in data
file while we fill temporary tables).

This is needed to preserve row order when scanning materialized cursors.
2013-09-06 15:59:19 +04:00
Sergey Petrunya
662bfed027 [SHOW] EXPLAIN UPDATE/DELETE, code re-structuring
- Merge with current 10.0-base
2013-08-24 00:46:49 +04:00
Ashish Agarwal
292aa926c1 WL#7076: Backporting wl6715 to support both formats
in 5.5, 5.6, 5.7.
2013-08-23 09:07:09 +05:30
Praveenkumar Hulakund
7fffec875a Bug#11765252 - READ OF FREED MEMORY WHEN "USE DB" AND
"SHOW PROCESSLIST"

Merging from 5.1 to 5.5
2013-08-21 10:44:22 +05:30
Praveenkumar Hulakund
3b1e98d218 Bug#11765252 - READ OF FREED MEMORY WHEN "USE DB" AND
"SHOW PROCESSLIST"

Analysis:
----------
The problem here is, if one connection changes its
default db and at the same time another connection executes
"SHOW PROCESSLIST", when it wants to read db of the another
connection then there is a chance of accessing the invalid
memory. 

The db name stored in THD is not guarded while changing user
DB and while reading the user DB in "SHOW PROCESSLIST".
So, if THD.db is freed by thd "owner" thread and if another
thread executing "SHOW PROCESSLIST" statement tries to read
and copy THD.db at the same time then we may endup in the issue
reported here.

Fix:
----------
Used mutex "LOCK_thd_data" to guard THD.db while freeing it
and while copying it to processlist.
2013-08-21 10:39:40 +05:30
Sergei Golubchik
a91a23858d cleanup
* use sql_mode_for_dates() where appropriate.
* always specify an argument for sql_mode_for_dates()
  (future-proof. easier to notice and fix if the caller
   will start using thd from a local variable or an argument)
2013-08-12 22:05:23 +02:00
prabakaran thirumalai
8412ac003c Bug#17083851 BACKPORT BUG#11765744 TO 5.1, 5.5 AND 5.6
Description:
Original fix Bug#11765744 changed mutex to read write lock
to avoid multiple recursive lock acquire operation on 
LOCK_status mutex.  
On Windows, locking read-write lock recursively is not safe. 
Slim read-write locks, which MySQL uses if they are supported by
Windows version, do not support recursion according to their 
documentation. For our own implementation of read-write lock, 
which is used in cases when Windows version doesn't support SRW,
recursive locking of read-write lock can easily lead to deadlock
if there are concurrent lock requests.
      
Fix:  
This patch reverts the previous fix for bug#11765744 that used
read-write locks. Instead problem of recursive locking for
LOCK_status mutex is solved by tracking recursion level using 
counter in THD object and acquiring lock only once when we enter 
fill_status() function first time.
2013-07-30 09:51:14 +05:30
prabakaran thirumalai
592a2b2a94 Bug#17083851 BACKPORT BUG#11765744 TO 5.1, 5.5 AND 5.6
Description:
Original fix Bug#11765744 changed mutex to read write lock
to avoid multiple recursive lock acquire operation on 
LOCK_status mutex.  
On Windows, locking read-write lock recursively is not safe. 
Slim read-write locks, which MySQL uses if they are supported by
Windows version, do not support recursion according to their 
documentation. For our own implementation of read-write lock, 
which is used in cases when Windows version doesn't support SRW,
recursive locking of read-write lock can easily lead to deadlock
if there are concurrent lock requests.

Fix:  
This patch reverts the previous fix for bug#11765744 that used
read-write locks. Instead problem of recursive locking for
LOCK_status mutex is solved by tracking recursion level using 
counter in THD object and acquiring lock only once when we enter 
fill_status() function first time.
2013-07-30 09:44:11 +05:30
Sergei Golubchik
b7b5f6f1ab 10.0-monty merge
includes:
* remove some remnants of "Bug#14521864: MYSQL 5.1 TO 5.5 BUGS PARTITIONING"
* introduce LOCK_share, now LOCK_ha_data is strictly for engines
* rea_create_table() always creates .par file (even in "frm-only" mode)
* fix a 5.6 bug, temp file leak on dummy ALTER TABLE
2013-07-21 16:39:19 +02:00
Sergei Golubchik
5f6380adde 10.0-base merge 2013-07-18 16:46:57 +02:00
Sergei Golubchik
97e640b9ae 5.5 merge 2013-07-17 21:24:29 +02:00
Sergei Golubchik
005c7e5421 mysql-5.5.32 merge 2013-07-16 19:09:54 +02:00
unknown
ba4b937af2 MDEV-4506: Parallel replication: Intermediate commit
Move the deferred event stuff from Relay_log_info to rpl_group_info
to make it thread safe for parallel replication.
2013-07-12 14:36:20 +02:00
unknown
f4d5dacf43 Merge the following patch from MySQL 5.6.10, in order to make perfschema.binlog_* tests work.
revno: 4559
committer: Marc Alff <marc.alff@oracle.com>
branch nick: mysql-5.6-bug14741537-v4
timestamp: Thu 2012-11-08 22:40:31 +0100
message:
  Bug#14741537 - MYSQL 5.6, GTID AND PERFORMANCE_SCHEMA
  
  Before this fix, statements using performance_schema tables:
  - were marked as unsafe for replication,
  - did cause warnings during execution,
  - were written to the binlog, either in STATEMENT or ROW format.
  
  When using replication with the new GTID feature,
  unsafe warnings are elevated to errors,
  which prevents to use both the performance_schema and GTID together.
  
  The root cause of the problem is not related to raising warnings/errors
  in some special cases, but deeper: statements involving the performance
  schema should not even be written to the binary log in the first place,
  because the content of the performance schema tables is 'local' to a server
  instance, and may differ greatly between nodes in a replication
  topology.
  
  In particular, the DBA should be able to configure (INSERT, UPDATE, DELETE)
  or flush (TRUNCATE) performance schema tables on one node,
  without affecting other nodes.
  
  This fix introduces the concept of a 'non-replicated' or 'local' table,
  and adjusts the replication logic to ignore tables that are not replicated
  when deciding if or how to log a statement to the binlog.
  
  Note that while this issue was detected using the performance_schema,
  other tables are also affected by the same problem.
  
  This fix define as 'local' the following tables, which are then never
  replicated:
  - performance_schema.*
  - mysql.general_log
  - mysql.slow_log
  - mysql.slave_relay_log_info
  - mysql.slave_master_info
  - mysql.slave_worker_info
  
  Existing behavior for information_schema.* is unchanged by this fix,
  to limit the scope of changes.
  
  Coding wise, this fix implements the following changes:
  
  1)
  
  Performance schema tables are not using any replication flags,
  since performance schema tables are not replicated.
  
  2)
  
  In open_table_from_share(),
  tables with no replication capabilities (performance_schema.*),
  tables with TABLE_CATEGORY_LOG (logs)
  and tables with TABLE_CATEGORY_RPL_INFO (replication)
  are marked as non replicated, with TABLE::no_replicate
  
  3)
  
  A new THD member, THD::m_binlog_filter_state,
  indicate if the current statement is written to the binlog
  (normal cases for most statements), or is to be discarded
  (because the statements affects non replicated tables).
  
  4)
  
  In THD::decide_logging_format(), the replication logic
  is changed to take into account non replicated tables.
  
  Statements that affect only non replicated tables are
  executed normally (no warning or errors), but not written
  to the binlog.
  
  Statements that affect (i.e., write to) a replicated table
  while also using (i.e., reading from or writing to) a non replicated table
  are executed normally in MIXED and ROW binlog format,
  and cause a new error in STATEMENT binlog format.
  
  THD::decide_logging_format() uses THD::m_binlog_filter_state
  to indicate if a statement is to be ignored, when writing to
  the binlog.
  
  5)
  
  In THD::binlog_query(), statements marked as ignored
  are not written to the binary log.
  
  6)
  
  For row based replication, the existing test for 'table->no_replicate',
  has been moved from binlog_log_row() to check_table_binlog_row_based().
2013-07-11 21:23:55 +03:00
unknown
31a5edb5c2 MDEV-4506: Parallel replication. Intermediate commit.
Hook in the wait-for-prior-commit logic (not really tested yet).
Clean up some resource maintenance around rpl_group_info (may still be some
smaller issues there though).
Add a ToDo list at the top of rpl_parallel.cc
2013-07-03 13:46:33 +02:00
Ashish Agarwal
e879caf845 WL#7076: Backporting wl6715 to support both formats in 5.5, 5.6, 5.7
Backporting wl6715 to mysql-5.5
2013-07-02 11:58:39 +05:30
Michael Widenius
82a0b8ae30 strict.test now works. 2013-07-02 22:11:12 +03:00
Michael Widenius
94d722b6a4 ha_partition.cc and ha_partition.h are now completely merged
Added sql_mode_t to simplify merges
2013-06-27 14:01:03 +03:00
unknown
e7606294b2 A fix of unions with duplicate rows and returning bug fix for lp:732124 union + limit returns wrong result 2013-06-26 13:17:27 +03:00
unknown
7e5dc4f074 MDEV-4506: Parallel replication. Intermediate commit.
Implement facility for the commit in one thread to wait for the commit of
another to complete first. The wait is done in a way that does not hinder
that a waiter and a waitee can group commit together with a single fsync()
in both binlog and InnoDB. The wait is done efficiently with respect to
locking.

The patch was originally made to support TaoBao parallel replication with
in-order commit; now it will be adapted to also be used for parallel
replication of group-committed transactions.

A waiter THD registers itself with a prior waitee THD. The waiter will then
complete its commit at the earliest in the same group commit of the waitee
(when using binlog). The wait can also be done explicitly by the waitee.
2013-06-26 12:10:35 +02:00
unknown
dfcc502ab5 Finished merging wl5986 started by Igor. 2013-06-19 14:32:14 +03:00
Sergey Petrunya
1c6fc3f6b9 [SHOW] EXPLAIN UPDATE/DELETE, code re-structuring
Part 2 of:
- Pass more tests
- select with subselects is now shown with type=PRIMARY where it used to be (incorrectly) 'SIMPLE'
2013-06-18 19:21:00 +04:00
Michael Widenius
8075b05b7d More merge fixes:
- mdl.cc and mdl.h merged completely
- mysql_system_tables*.sql merged completely
- Fixed wrong merge of lock_tables
- Added some missing functions:
 - bool THD::notify_shared_lock()
 - Dynamic_array::pop, Dynamic_array::del
- Added MDL_context_owner to THD
- Added metadata_locks_hash_instances
2013-06-16 21:26:40 +03:00
Michael Widenius
5f1f2fc0e4 Applied all changes from Igor and Sanja 2013-06-15 18:32:08 +03:00
Sergei Golubchik
dacb3809a2 MDEV-4422 SHOW PROCESSLIST reference to THD::db not protected against simultaneous updates
protect THD::db with THD::LOCK_thd_data
2013-06-12 20:29:19 +02:00
Igor Babaev
cd0e834d12 Merge 10.0-base -> 10.0 2013-04-22 20:55:22 -07:00
unknown
9441e53653 MDEV-4345
Sampling of selectivity of LIKE predicate.
2013-04-18 22:22:04 +03:00
Igor Babaev
a1cd28e2e5 Merge 10.0-base -> 10.0 2013-04-17 10:18:04 -07:00
unknown
0e7410a154 Merge 10.0-base -> 10.0 (GTID). 2013-04-17 15:17:01 +02:00
Lixun Peng
82eedf4e97 Makeing rpl_filter for each Master_info.
Users can set different repplication filter rules for each replication connection, in my.cnf or command line.
But the rules set online will not record in master.info, it means if users restart MySQL, these rules will lose.
So if users wantn't their replication filter rules lose, they should write the rules in my.cnf.

Users can set rules by 2 ways:
1. Online SET command, "SET connection_name.replication_filter_settings = rules;".
2. In my.cnf, "connection_name.replication_filter_settings = rules".

If no connection_name in my.cnf, this rule will apply for ALL replication connection.
If no connetion_name in SET statement, this rull will apply for default_connection_name.
2013-04-16 19:43:28 +08:00
Igor Babaev
f4cd2b37b1 Merge 10.0-base -> mwl253 2013-04-15 09:16:54 -07:00
Sergei Golubchik
a9035be5b7 10.0-base merge 2013-04-15 15:09:22 +02:00
unknown
665a31af2b MDEV-26: Global transaction ID. First alpha release.
Merge of 10.0-mdev26 feature tree into 10.0-base.

Global transaction ID is prepended to each event group in the binlog.

Slave connect can request to start from GTID position instead of specifying
file name/offset of master binlog. This facilitates easy switch to a new
master.

Slave GTID state is stored in a table mysql.rpl_slave_state, which can be
InnoDB to get crash-safe slave state.

GTID includes a replication domain ID, allowing to keep track of distinct
positions for each of multiple masters.
2013-04-15 10:55:27 +02:00