Changeset: 6503f938b5fe for MonetDB
URL: http://dev.monetdb.org/hg/MonetDB?cmd=changeset;node=6503f938b5fe
Modified Files:
monetdb5/modules/mal/wlc.c
sql/backends/monet5/wlr.c
Branch: wlcr
Log Message:
Documentation
diffs (113 lines):
diff --git a/monetdb5/modules/mal/wlc.c b/monetdb5/modules/mal/wlc.c
--- a/monetdb5/modules/mal/wlc.c
+++ b/monetdb5/modules/mal/wlc.c
@@ -30,11 +30,11 @@
* with a time-bounded delay. This means that both master and replica run at a
certain beat
* (in seconds) by which information is made available or read by the replica.
*
- * Such a replica in query workload sharing, database versioning, and
(re-)partitioning.
- * Tables taken from the master are not protected against local updates in the
clone.
+ * Such a replica is used in query workload sharing, database versioning, and
(re-)partitioning.
+ * Tables taken from the master are not protected against local updates in the
replica.
* However, any replay transaction that fails stops the cloning process.
* Furthermore, only persistent tables are considered for replication.
- * Updates under the 'tmp' schema are ignored.
+ * Updates under the 'tmp' schema, i.e. temporary tables, are ignored.
*
* Simplicity and ease of end-user control has been the driving argument here.
*
@@ -45,11 +45,12 @@
*
* A database can be set into 'master' mode only once using the SQL command:
* CALL master()
- * An alternative path to the log records can be given to reduce the IO
latency,
- * e.g. using a nearby SSD.
- * By default, it creates a directory .../dbfarm/dbname/wlc_logs to hold all
- * necessary information for the creation of a database clone and
- * a configuration file .../dbfarm/dbname/wlc.config to hold the state of the
transaction logs.
+ * An optional path to the log record directory can be given to reduce the IO
latency,
+ * e.g. using a nearby SSD, or where there is ample of space to keep a long
history,
+ * e.g. a HDD or cold storage location.
+ *
+ * By default, the command creates a directory .../dbfarm/dbname/wlc_logs to
hold all logs
+ * and a configuration file .../dbfarm/dbname/wlc.config to hold the state of
the transaction logs.
* It contains the following key=value pairs:
* snapshot=<path to a snapshot directory>
* logs=<path to the wlc log directory>
@@ -65,12 +66,11 @@
* The log records are represented as ordinary MAL statement blocks, which
* are executed in serial mode. (parallelism can be considered for large
updates later)
* Each transaction job is identified by a unique id, its starting time, and
the user responsible..
- * The log-record should end with a commit.
+ * The log-record should end with a commit to be allowed for re-execution.
+ * Log records with a rollback tag are merely for analysis by the DBA.
*
- * A transaction log is created by the master using a heartbeat (in seconds).
- * A new transaction log file is published when the system has been
- * collecting logs for some time.
- * The cycle time determines the drift of the replica, excluding its own speed
to catch up.
+ * A transaction log file is created by the master using a heartbeat (in
seconds).
+ * A new transaction log file is published when the system has been collecting
transaction records for some time.
* The beat can be set using a SQL command, e.g.
* CALL masterbeat(duration)
* Setting it to zero leads to a log file per transaction and may cause a
large log directory.
@@ -85,9 +85,15 @@
* CALL stopmaster().
* It typically is the end-of-life-time for a snapshot. For example, when
planning to do
* a large bulk load of the database, stopping logging avoids a double write
into the
- * database. The database can be brought back into wlc mode using a fresh
snapshot.
+ * database. The database can only be brought back into master mode using a
fresh snapshot.
*
- *[TODO] A more secure way to set a database into master mode is to use the
command
+ * One of the key challenges for a DBA is to keep the log directory
manageable, because it grows
+ * with the speed up updates being applied to the database. This calls for
regularly checking
+ * for their disk footprint and taking a new snapshot as a frame of reference.
+ *
+ * The DBA tool 'monetdb' provides options to create a master and its replicas.
+ * It will also maintain the list of replicas for inspection and managing
their drift.
+ * For example,
* monetdb master <dbname> [ <optional snapshot path>]
* which locks the database, takes a save copy, initializes the state chance
to master.
*
@@ -101,7 +107,7 @@
*
* Every clone should start off with a copy of the binary snapshot identified
by 'snapshot'.
* A fresh database can be turned into a clone using the call
- * CALL replicate('mastername')
+ * CALL replicate('mastername')
* It will grab the latest snapshot of the master and applies all
* available log files before releasing the system. Progress of
* the replication can be monitored using the -fraw option in mclient.
diff --git a/sql/backends/monet5/wlr.c b/sql/backends/monet5/wlr.c
--- a/sql/backends/monet5/wlr.c
+++ b/sql/backends/monet5/wlr.c
@@ -212,7 +212,9 @@ WLRprocess(void *arg)
mnstr_printf(GDKerr, "!WARNING: could not read %s\n",
path);
c->yycur = 0;
+#ifdef _WLR_DEBUG_
mnstr_printf(cntxt->fdout,"#replay log file:%s\n",path);
+#endif
// now parse the file line by line to reconstruct the WLR blocks
do{
@@ -234,7 +236,9 @@ WLRprocess(void *arg)
( wlr_timelimit[0] && strcmp(getVarConstant(mb,
getArg(q,2)).val.sval, wlr_timelimit) >= 0))
){
/* stop execution of the transactions if your
reached the limit */
+#ifdef _WLR_DEBUG_
mnstr_printf(GDKerr,"#skip tlimit %s tag
%s\n", wlr_timelimit,getVarConstant(mb, getArg(q,2)).val.sval);
+#endif
resetMalBlk(mb, 1);
trimMalVariables(mb, NULL);
goto wrapup;
@@ -242,7 +246,9 @@ WLRprocess(void *arg)
if( getModuleId(q) == wlrRef && getFunctionId(q) ==
transactionRef ){
strncpy(wlr_read, getVarConstant(mb,
getArg(q,2)).val.sval,26);
wlr_tag = getVarConstant(mb,
getArg(q,1)).val.lval;
+#ifdef _WLR_DEBUG_
mnstr_printf(GDKerr,"#run tlimit %s tag %s\n",
wlr_timelimit, wlr_read);
+#endif
}
// only re-execute successful transactions.
if ( getModuleId(q) == wlrRef && getFunctionId(q)
==commitRef ){
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