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I did not find any legitimate use of "can not", however skipped
changing e.g RFCs archived in the source tree.
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make erlang:process_info/1 not retrieve messages
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process_info/1 retrieves a number of properties related to a process,
including the list of messages in its mailbox. This is potentially
unsafe if the target process has a large number of queued messages:
- there is no a priori upper bound on the amount of memory being
allocated to hold that list, and
- the loop to retrieve the messages is uninterruptible, so the
Erlang scheduler where this executes blocks for the duration
We've seen process_info/1 bring down heavily loaded nodes on more
than one occasion. At least once it appeared to have blocked the
Erlang heart process from executing, causing the external heart to
kill the VM.
Consequently this removes 'messages' from the list of process_info
tags to retrieve for process_info/1. Note that process_info/1 still
retrieves 'message_queue_len', and process_info/2 can still retrieve
'messages' when asked to.
A few places in the OTP libraries need minor adjustments, since they
want 'message_queue_len' but compute it from the length of the list
of messages.
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Take care of the call of erlang:get_stacktrace() in
module mnesia_lib.
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The remaining call (in module mnesia_lib) is taken care
of in the following commit.
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Helps when mnesia_tm gets drowned in dirty_writes from remote node.
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Worker processes can cause error reports if the main mnesia processes
dissapear.
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* dgud/mnesia/ext-backend/PR-858/OTP-13058:
mnesia_ext: Add basic backend extension tests
mnesia_ext: reuse snmp field for ext updates
mnesia_ext: Create table/data containers from mnesia monitor not temporary processes
mnesia_ext: Implement ext copies index
mnesia_ext: Load table ext
mnesia_ext: Dumper and schema changes
mnesia_ext: Refactor mnesia_schema.erl
mnesia_ext: Ext support in fragmented tables
mnesia_ext: Backup handling
mnesia_ext: Create schema functionality
mnesia_ext: Add ext copies and db_fold to low level api
mnesia_ext: Refactor record_validation code
mnesia_ext: Add create_external and increase protocol version to monitor
mnesia_ext: Add ext copies to records
mnesia_ext: Add supervisor and behaviour modules
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Minimal impact when talking to older nodes.
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Make ram_copies index always use ordered_set
And use index type as prefered type not a implementation requirement,
the standard implmentation will currently ignore the prefered type.
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* henrik/update-copyrightyear:
update copyright-year
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Mnesia didn't forward mnesia_down to transactions which where already
decided to be aborted, but that could lead to hanging transactions
still waiting for messages from the node which had stopped.
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Avoids building stacktraces where it is not needed and do
not mask errors, i.e. only catch the relevant classes in each try.
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Bad timing could lead to hanging transactions after a mnesia down from a
node with sticky locks.
Excellent bug report from janchochol
Situation:
* node A and B have copies of table T
* node A ows sticky of table T
* node A goes down (e.g. crash)
* node B tries to perform transactional operation on table T
(e.g. mnesia:select)
In this situation there is possibility that first (and maybe other)
transaction on node B will hang indefinitely.
This is caused by race condition, when transaction process send lock
request operation to node A and waits for reply. When node A is down
it will never send reply, so process on node B will be stuck
forever.
Reason is that message sent to mnesia_locker gen_server from
mnesia_locker:mnesia_down can be received after mnesia_locker gen_server
already replies to transaction processes with {switch, N, Req} and
node N is down.
Monitoring remote process when sending request to other node should
be safe solution.
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timer:send_interval behaves badly when resuming from sleep on some
platforms. For example, if I sleep for 10 minutes, and have a
send_interval running once per minute, when I resume, 10 messages
will be sent immediately, eliminating the benefit of only running
the work periodically. This is admittedly a separate bug with
send_interval, but the workaround is straightforward, and also
protects from messages piling up in the queue when the work takes
longer than the interval.
This patch fixes piled up error reports on resume from sleep:
** WARNING ** Mnesia is overloaded: {dump_log, write_threshold}
You'll still be warned if mnesia is overloaded, just not repeatedly.
Additionally, erlang:send_after is more efficient than using the
timer module equivalent [1]
[1] http://www.erlang.org/doc/efficiency_guide/commoncaveats.html#id57251
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Since the table loader also sets (table) write locks, a special
lock type, 'load', was needed. Unfortunately, this affects mnesia
activity callbacks that redefine the lock operation.
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With {majority, true} set for a table, write transactions will
abort if they cannot commit to a majority of the nodes that
have a copy of the table. Currently, the implementation hooks
into the prepare_commit, and forces an asymmetric transaction
if the commit set affects any table with the majority flag set.
In the commit itself, the transaction will abort if it cannot
satisfy the majority requirement for all tables involved in the
thransaction.
A future optimization might be to abort already when a write
lock is attempted on such a table (/-object) and the lock cannot
be set on enough nodes.
This functionality introduces the possibility to automatically
"fence off" a table in the presence of failures.
This is a first implementation. Only basic tests have been
performed.
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With help from Kostis
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A process that calls mnesia:subscribe(activity) will receive the message:
{mnesia_activity_event, ActivityID, complete}
when any activity that caused a change to a database has finished
committing its changes. This allows a subscriber to collect messages
already available through the mnesia:subscribe({table, ...}) system
to group them as completed transactions.
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invoking mnesia:sync_transaction/[1,2]. Thanks Igor Ribeiro
Sucupira.
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