serialnumber within the transaction to order the messages correctly. The
defaultmaximum message size is 50,000 bytes, but you can use the Message
Agent-l option to change this setting.
Sendingmessages Thelog_sent column holds the local transaction log offset for the latest
messagesent to the subscriber. Whenthe Message Agent sends a message, it
setsthe log_sent value to the offset of the last COMMIT in the message.
Oncethe message has been received and applied at the subscribed database,
confirmationis sent back to the publisher. When the publisher Message
Agentreceives the confirmation, it sets the confirm_sent column for that
subscriberwith the local transaction log offset. Both log_sent and
confirm_sentare offsets in the local database transaction log, and
confirm_sentcannot be a later offset than log_sent.
Receivingmessages Whenthe Message Agent at a subscriber database receives and applies a
replicationupdate, it updates the log_received column with the offset of the
lastCOMMIT in the message. The log_received column at any subscriber
databasetherefore contains a transaction log offset in the publisher
database’stransaction log. After the operations havebeen received and
applied,the Message Agent sends confirmation back to the publisher
databaseand also sets the confirm_received value in the local
SYSREMOTEUSERtable. The confirm_receivedcolumn at any subscriber
databasecontains a transaction log offset in the publisher database’s
transactionlog.
Subscriptions are
two-way SQLRemote subscriptions are two-way operations: each remote database is
asubscriber to publications of the consolidated database and the
consolidateddatabase subscribes to a matching publication from each
remotedatabase. Therefore, the remoteuser SQL Remote system tables at
theconsolidated and remote database hold complementary information.
TheMessage Agent applies transactions and updates the log_received value
atomically.If a message contains several transactions, and a failure occurs
whilea message is being applied, the log_received value corresponds
exactlyto what has been applied and committed.
Resendingmessages Theremoteuser SQL Remote table contains two other columns that handle
resendingmessages. The resend_count and rereceive_countcolumns are
retrycounts that are incremented when messages get lost or deleted for some
reason.
Ingeneral, the log_send column has the same value as the log_sent column.
However,if the log_send has a value that is greater than log_sent, the
MessageAgent sends messages to the subscriber immediately on its next
run.
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