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Mailbox Transactions
====================

Before you can read any mails or do any changes to mails, you need to create a
transaction with 'mailbox_transaction_begin()'. It has a few flags:

 * 'MAILBOX_TRANSACTION_FLAG_HIDE': Mark the changes in a way that when later
   <syncing> [Design.Storage.Mailbox.Sync.txt] the mailbox in this session,
   'mailbox_sync_next()' won't return sync records for the changes done by this
   transaction. This is primarily meant for flag and keyword changes, you can't
   hide expunges. For example IMAP's 'STORE FLAGS.SILENT' command is
   implemented by setting this flag for the transaction.
 * 'MAILBOX_TRANSACTION_FLAG_EXTERNAL': Changes done by this transaction should
   be marked as external changes. Internal changes can be thought of as "change
   requests" that syncing later finishes, while external changes are done
   immediately and syncing ignores them. Normally you would use this flag when
   you want to save or copy messages, nothing else.
 * 'MAILBOX_TRANSACTION_FLAG_ASSIGN_UIDS': Require assigning UIDs to
   saved/copied messages immediately. Normally this is done only when it's easy
   (maildir: if dovecot-uidlist can be locked without waiting, mbox: if mbox is
   already fully synced).
 * 'MAILBOX_TRANSACTION_FLAG_REFRESH': Do a quick index refresh, so any recent
   flag/modseq changes done by other Dovecot sessions will be visible. You
   shouldn't usually need this, because usually you should have recently done a
   mailbox sync.

Changes for a transaction are kept in memory until the transaction is
committed. If you want to cancel the changes, you can call
'mailbox_transaction_rollback()'. Transaction can be commited with
'mailbox_transaction_commit()'. If you want to know a bit more about the
results of the transaction, use 'mailbox_transaction_commit_get_changes()'
instead. It returns a change structure:

 * uid_validity: UIDVALIDITY used by returned UIDs
 * saved_uids: UIDs assigned to saved/copied mails. Typically they're in an
   ascending order, unless you explicitly requested some specific UIDs for
   mails while saving them (e.g. dsync does this).
 * ignored_uid_changes: Number of UIDs that couldn't be changed by
   'mail_update_uid()' calls, because the UIDs were less than next_uid's value.

 * ignored_modseq_changes: Number of modseqs that couldn't be changed by
   'mail_update_modseq()' calls, because they would have lowered the modseq.

Once you're done with reading the change structure, be sure to free the memory
used by it with 'pool_unref(&changes->pool)'.

'mailbox_transaction_set_max_modseq()' can be used to implement atomic
conditional flag changes. If message's modseq is higher than the given
max_modseq while transaction is being committed, the change isn't done and the
message's sequence number is added to the given array.

(This file was created from the wiki on 2019-06-19 12:42)
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