Distributed Storage Functions
- Yeok Hong Ng
The Distributed Storage Profile enables you to access a distributed storage solution from APL without having to provide details about its type or implementation.
The APL functions described in this section use a key-value model to read, store and remove data via the specified profile. The functions can optionally use sessions that are either committed or rolled back in order to secure transaction consistency.
The following functions for Distributed Storage described here are:
- 1 dsInitStorage
- 2 dsStore
- 3 dsStoreUdr
- 4 dsStoreMany
- 5 dsStoreManyUdrs
- 6 dsCommand
- 7 dsRemove
- 8 dsRemoveMany
- 9 dsRead
- 10 dsReadUdr
- 11 dsReadMany
- 12 dsReadManyUdrs
- 13 dsBeginTransaction
- 14 dsCommitTransaction
- 15 dsRollbackTransaction
- 16 dsCreateKeyIterator
- 17 dsCreateREKeyIterator
- 18 dsGetNextKey
- 19 dsDestroyKeyIterator
- 20 dsLastErrorMessage
Initializing Storage
dsInitStorage
The dsInitStorage function returns a Distributed Storage Profile object that is used in subsequent APL calls to distributed storage functions.
any dsInitStorage(string profid)Parameter | Description |
|---|---|
profid | A string containing a reference to a Distributed Storage Profile. |
Returns | A Distributed Storage Profile object. |
Example - Using dsInitStorage
any storage=null;
initialize { storage = dsInitStorage("default.ds_profile"); if(null != dsLastErrorMessage()) { //Error Handling }}
Note!
The dsInitStorage function must be used in the initialize block and not consume block.
Storing and Removing Data
The following functions enable you to perform changes on data in a distributed storage:
dsStoredsStoreUdrdsStoreManydsStoreManyUdrsdsRemovedsRemoveMany
dsStore
The dsStore function stores a key-value pair in a distributed storage.
void dsStore(
any profid,
string key,
bytearray value,
any transid)Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
key | The key of a key-value pair. |
value | The value of a key-value pair. |
transid | The transaction identifier that is returned by dsBeginTransaction. Use a null value to store data in non-transaction mode. If the identifier is set the transaction is completed by calling dsCommitTransaction. |
Returns | Nothing. |
Example - Using dsStore
any storage = null;
initialize {
storage = dsInitStorage("default.ds_profile");
if(null != dsLastErrorMessage()) {
//Error Handling
}
}
consume {
bytearray myValue = null;
strToBA(myValue, "123");
dsStore(storage, "mykey", myValue, null);
if(null != dsLastErrorMessage()) {
//Error Handling
}
}dsStoreUdr
The dsStoreUdr function stores a key-value pair in a distributed storage.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
key | The key of a key-value pair. |
myUDR | The UDR to be stored. |
transid | The transaction identifier that is returned by dsBeginTransaction. Use a null value to store data in non-transaction mode. If the identifier is set the transaction is completed by calling dsCommitTransaction. |
Returns | Nothing. |
dsStoreMany
The dsStoreMany function stores a set of key-value pairs in a distributed storage.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
values | The key-value pairs to store. |
transid | The transaction identifier that is returned by dsBeginTransaction. Use a null value to store data in non-transaction mode. If the identifier is set the transaction is completed by calling dsCommitTransaction. |
Returns | Nothing. |
dsStoreManyUdrs
The dsStoreManyUdrs function stores a set of key-value pairs in a distributed storage.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
myUDRs | The key-value pairs to store. |
transid | The transaction identifier that is returned by dsBeginTransaction. Use a null value to store data in non-transaction mode. If the identifier is set the transaction is completed by calling dsCommitTransaction. |
Returns | Nothing. |
dsCommand
The dsCommand function stores data with a Time To Live (TTL) on the entry by updating the ‘expiration’ field for data in Couchbase, meaning it will be removed when it gets too old.
You can also use the dsCommand to extend the expiration field of the data in Couchbase using the “touch” action.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
action | The action you want to perform, “ttlStore” for storing UDRs with TTL or “touch“ to extend the TTL. |
key | The key of a key-value pair. |
ttl | Time To Live in seconds. |
myUDR | The UDR to be stored. |
Returns | Nothing. |
dsRemove
The dsRemove function removes a key-value pair, identified by a key, from a distributed storage.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
key | The key of the key-value pair to remove. |
transid | The transaction identifier that is returned by dsBeginTransaction. Use a null value to remove data in non-transaction mode. If the identifier is set the transaction is completed by calling dsCommitTransaction. |
Returns | Nothing. |
dsRemoveMany
The dsRemoveMany function removes a list of key-value pairs, identified by a list of keys, from a distributed storage.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
keys | The keys of the key-value pairs to remove. |
transid | The transaction identifier that is returned by dsBeginTransaction. Use a null value to remove data in non-transaction mode. If the identifier is set the transaction is completed by calling dsCommitTransaction. |
Returns | Nothing. |
Reading Data
The following functions enable you to read data from a distributed storage.
dsReaddsReadUdrdsReadManydsReadManyUdrs
dsRead
The dsRead function reads a value, identified by a key, from a distributed storage.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
key | The key of a key-value pair. |
transid | The transaction identifier that is returned by dsBeginTransaction. Use a null value to read data in non-transaction mode. If the identifier is set, the read key-value pair is locked for other transactions untildsCommitTransaction or dsRollbackTransaction is called. |
Returns | A bytearray containing the value of a key-value pair. |
dsReadUdr
The dsReadUdr function reads a set of UDRs, identified by a list of keys, from a distributed storage.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
key | The key of a key-value pair. |
transid | The transaction identifier that is returned by dsBeginTransaction. Use a null value to read data in non-transaction mode. If the identifier is set, the read key-value pair is locked for other transactions untildsCommitTransaction or dsRollbackTransaction is called. |
Returns | A UDR identified by the key parameter. |
dsReadMany
The dsReadMany function reads a set of key-value pairs, identified by a list of keys, from a distributed storage.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
keys | The keys of the key-value pairs to be read. |
transid | The transaction identifier that is returned by dsBeginTransaction. Use a null value to read data in non-transaction mode. If the identifier is set, the read key-value pairs are locked for other transactions untildsCommitTransaction or dsRollbackTransaction is called. |
Returns | A map containing the key-value pairs. |
dsReadManyUdrs
The dsReadManyUdrs function reads a key-value map, identified by a key, from a distributed storage.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
keys | The keys of the key-value pairs to be read. |
transid | The transaction identifier that is returned by dsBeginTransaction. Use a null value to read data in non-transaction mode. If the identifier is set, the read key-value pairs are locked for other transactions untildsCommitTransaction or dsRollbackTransaction is called. |
Returns | A map containing the key-value pairs. |
Transaction Functions
The following functions provide transaction safety by performing commit or rollback on a set of calls to a Distributed Storage Profile:
dsBeginTransactiondsCommitTransactiondsRollbackTransaction
dsBeginTransaction
The dsBeginTransaction function begins a new transaction and returns an object that can be used in subsequent APL calls to distributed storage functions.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
Returns | A transaction identifier. |
dsCommitTransaction
The dsCommitTransaction function ends a transaction and commits changes that has been made using the specified transaction identifier.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
transid | The transaction identifier that is returned by dsBeginTransaction. |
Returns | Nothing. |
dsRollbackTransaction
The dsRollbackTransaction function ends a transaction and reverts changes that has been made using the specified transaction identifier.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
transid | The transaction identifier that is returned by dsBeginTransaction. |
Returns | Nothing. |
Iterator Functions
The following functions are used for traversing through a set of keys in a distributed storage:
dsCreateKeyIteratordsCreateREKeyIteratordsGetNextKeydsDestroyKeyIterator
dsCreateKeyIterator
The dsCreateKeyIterator function creates an iterator object that is used in subsequent APL calls to other iterator functions.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
startkey | The key to start iterating at. |
stopkey | The key to finish iterating at. |
Returns | An iterator object used in subsequent APL calls to dsGetNextKey and dsDestroyKeyIterator.7.5.2. dsGetNextKey. |
dsCreateREKeyIterator
The dsCreateREKeyIterator function creates an iterator object that is used in subsequent APL calls to other iterator functions.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
searchpattern | A search pattern which may include wild card '*'. |
Returns | An iterator object used in subsequent APL calls to dsGetNextKey and dsDestroyKeyIterator. |
dsGetNextKey
The dsGetNextKey function gets the next available key from a distributed storage using an iterator object. Each subsequent call to the function returns the next key in the iterator's range.
Parameter | Description |
|---|---|
profid | The Distributed Storage Profile. |
iterator | The iterator object returned by dsCreateKeyIterator. |
Returns | The key of a key-value pair. A null value is returned if a key cannot be found. |
dsDestroyKeyIterator
The dsDestroyKeyIterator function destroys an iterator object created with dsCreateKeyIterator in order to free up memory. It is good practice to always include a call to this function in the APL code though it may not be required for all types of storage.
Parameter | Description |
|---|---|
profid | The Distributed Storage profile. |
iterator | The iterator object returned by dsCreateKeyIterator. |
Returns | Nothing |
Error Handling
dsLastErrorMessage
The dsLastErrorMessage function returns the error message from the last call to a distributed storage function. Distributed storage functions that are not used for error handling, do not return error codes and generally do not cause runtime errors. For this reason, The dsLastErrorMessage function must be called after each operation to validate success.
Parameter | Description |
|---|---|
Returns | An error message, or null if no error has occurred since the last call to this function. The content of message depends on the type of profile that is used with the Distributed Storage profile. For example, with a Couchbase profile, the error message is identical to the error message exposed by the Couchbase API. |