Improve code comments
Author: Erik Rijkers <er@xs4all.nl>
This commit is contained in:
Peter Eisentraut
parent
ae1aa28eb6
commit
88c6cff8e7
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@ -12,18 +12,18 @@
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* logical replication.
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*
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* The initial data synchronization is done separately for each table,
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* in separate apply worker that only fetches the initial snapshot data
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* from the publisher and then synchronizes the position in stream with
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* in a separate apply worker that only fetches the initial snapshot data
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* from the publisher and then synchronizes the position in the stream with
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* the main apply worker.
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*
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* The are several reasons for doing the synchronization this way:
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* There are several reasons for doing the synchronization this way:
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* - It allows us to parallelize the initial data synchronization
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* which lowers the time needed for it to happen.
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* - The initial synchronization does not have to hold the xid and LSN
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* for the time it takes to copy data of all tables, causing less
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* bloat and lower disk consumption compared to doing the
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* synchronization in single process for whole database.
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* - It allows us to synchronize the tables added after the initial
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* synchronization in a single process for the whole database.
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* - It allows us to synchronize any tables added after the initial
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* synchronization has finished.
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*
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* The stream position synchronization works in multiple steps.
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@ -147,7 +147,7 @@ finish_sync_worker(void)
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}
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/*
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* Wait until the relation synchronization state is set in catalog to the
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* Wait until the relation synchronization state is set in the catalog to the
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* expected one.
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*
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* Used when transitioning from CATCHUP state to SYNCDONE.
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@ -206,12 +206,12 @@ wait_for_relation_state_change(Oid relid, char expected_state)
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}
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/*
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* Wait until the the apply worker changes the state of our synchronization
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* Wait until the apply worker changes the state of our synchronization
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* worker to the expected one.
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*
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* Used when transitioning from SYNCWAIT state to CATCHUP.
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*
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* Returns false if the apply worker has disappeared or table state has been
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* Returns false if the apply worker has disappeared or the table state has been
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* reset.
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*/
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static bool
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@ -225,7 +225,7 @@ wait_for_worker_state_change(char expected_state)
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CHECK_FOR_INTERRUPTS();
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/* Bail if he apply has died. */
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/* Bail if the apply has died. */
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LWLockAcquire(LogicalRepWorkerLock, LW_SHARED);
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worker = logicalrep_worker_find(MyLogicalRepWorker->subid,
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InvalidOid, false);
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@ -333,7 +333,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
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Assert(!IsTransactionState());
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/* We need up to date sync state info for subscription tables here. */
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/* We need up-to-date sync state info for subscription tables here. */
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if (!table_states_valid)
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{
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MemoryContext oldctx;
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@ -365,7 +365,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
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}
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/*
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* Prepare hash table for tracking last start times of workers, to avoid
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* Prepare a hash table for tracking last start times of workers, to avoid
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* immediate restarts. We don't need it if there are no tables that need
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* syncing.
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*/
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@ -401,7 +401,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
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{
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/*
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* Apply has caught up to the position where the table sync has
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* finished. Time to mark the table as ready so that apply will
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* finished. Mark the table as ready so that the apply will
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* just continue to replicate it normally.
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*/
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if (current_lsn >= rstate->lsn)
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@ -436,7 +436,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
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else
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/*
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* If no sync worker for this table yet, count running sync
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* If there is no sync worker for this table yet, count running sync
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* workers for this subscription, while we have the lock, for
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* later.
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*/
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@ -477,7 +477,7 @@ process_syncing_tables_for_apply(XLogRecPtr current_lsn)
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/*
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* If there is no sync worker registered for the table and there
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* is some free sync worker slot, start new sync worker for the
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* is some free sync worker slot, start a new sync worker for the
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* table.
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*/
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else if (!syncworker && nsyncworkers < max_sync_workers_per_subscription)
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@ -551,7 +551,7 @@ copy_read_data(void *outbuf, int minread, int maxread)
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int bytesread = 0;
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int avail;
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/* If there are some leftover data from previous read, use them. */
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/* If there are some leftover data from previous read, use it. */
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avail = copybuf->len - copybuf->cursor;
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if (avail)
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{
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@ -694,7 +694,7 @@ fetch_remote_table_info(char *nspname, char *relname,
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(errmsg("could not fetch table info for table \"%s.%s\": %s",
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nspname, relname, res->err)));
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/* We don't know number of rows coming, so allocate enough space. */
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/* We don't know the number of rows coming, so allocate enough space. */
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lrel->attnames = palloc0(MaxTupleAttributeNumber * sizeof(char *));
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lrel->atttyps = palloc0(MaxTupleAttributeNumber * sizeof(Oid));
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lrel->attkeys = NULL;
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@ -852,22 +852,22 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
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pgstat_report_stat(false);
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/*
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* We want to do the table data sync in single transaction.
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* We want to do the table data sync in a single transaction.
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*/
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StartTransactionCommand();
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/*
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* Use standard write lock here. It might be better to
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* disallow access to table while it's being synchronized. But
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* Use a standard write lock here. It might be better to
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* disallow access to the table while it's being synchronized. But
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* we don't want to block the main apply process from working
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* and it has to open relation in RowExclusiveLock when
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* and it has to open the relation in RowExclusiveLock when
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* remapping remote relation id to local one.
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*/
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rel = heap_open(MyLogicalRepWorker->relid, RowExclusiveLock);
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/*
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* Create temporary slot for the sync process. We do this
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* inside transaction so that we can use the snapshot made by
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* Create a temporary slot for the sync process. We do this
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* inside the transaction so that we can use the snapshot made by
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* the slot to get existing data.
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*/
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res = walrcv_exec(wrconn,
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@ -883,7 +883,7 @@ LogicalRepSyncTableStart(XLogRecPtr *origin_startpos)
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* Create new temporary logical decoding slot.
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*
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* We'll use slot for data copy so make sure the snapshot is
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* used for the transaction, that way the COPY will get data
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* used for the transaction; that way the COPY will get data
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* that is consistent with the lsn used by the slot to start
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* decoding.
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*/
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