The most common mechanism type in database systems since their early days in the 1970s has been Strong strict Two-phase locking ( SS2PL ; also called Rigorous scheduling or Rigorous 2PL ) which is a special case ( variant ) of both Two-phase locking ( 2PL ) and Commitment ordering ( CO ).

In spite of its long name ( for historical reasons ) the idea of the SS2PL mechanism is simple: " Release all locks applied by a transaction only after the transaction has ended.

SS2PL mentioned above is a variant ( special case ) of CO and thus also effective to achieve distributed and global serializability.

However, SS2PL is blocking and constraining ( pessimistic ), and with the proliferation of distribution and utilization of systems different from traditional database systems ( e. g., as in Cloud computing ), less constraining types of CO ( e. g., Optimistic CO ) may be needed for better performance.

Differently from the general Distributed CO, Distributed SS2PL exists automatically when all local components are SS2PL based ( in each component CO exists, implied, and the vote ordering strategy is now met automatically ).

This fact has been known and utilized since the 1980s ( i. e., that SS2PL exists globally, without knowing about CO ) for efficient Distributed SS2PL, which implies Distributed serializability and strictness ( e. g., see Raz 1992, page 293 ; it is also implied in Bernstein et al.

As has been mentioned above, Distributed SS2PL, including Distributed strictness ( recoverability ) and Distributed commitment ordering ( serializability ), automatically employs the needed vote ordering strategy, and is achieved ( globally ) when employed locally in each ( local ) database system ( as has been known and utilized for many years ; as a matter of fact locality is defined by the boundary of a 2PC participant ( Raz 1992 ) ).

2PL is a superset of strong strict two-phase locking ( SS2PL ), also called rigorousness, which has been widely utilized for concurrency control in general-purpose database systems since the 1970s.

SS2PL was called strict 2PL but this name usage is not recommended now.

Now strict 2PL ( S2PL ) is the intersection of strictness and 2PL, which is different from SS2PL.

SS2PL is also a special case of commitment ordering, and inherits many of CO's useful properties.

What has made SS2PL so popular ( probably the most utilized serializability mechanism ) is the effective and efficient locking-based combination of two ingredients ( the first does not exist in both general 2PL and S2PL ; the second does not exist in general 2PL ):

Additionally SS2PL is easier, with less overhead to implement than both 2PL and S2PL, provides exactly same locking, but sometimes releases locks later.

However, practically ( though not simplistically theoretically ) such later lock release occurs only slightly later, and this apparent disadvantage is insignificant and disappears next to the advantages of SS2PL.

Thus, the importance of the general Two-phase locking ( 2PL ) is historic only, while Strong strict two-phase locking ( SS2PL ) is practically the important mechanism and resulting schedule property.

SS2PL actually comprises only one phase: phase-2 does not exist, and all locks are released only after transaction end.

In practice most commercial database systems use strong strict two phase locking ( SS2PL ) for concurrency control, which ensures global serializability, if all the participating databases employ it.

Less constrained Distributed serializability and strictness can be efficiently achieved by Distributed Strict CO ( SCO ), or by a mix of SS2PL based and SCO based local components.

Thus 2PL by itself does not seem to have much practical importance, and whenever 2PL or S2PL utilization has been mentioned in the literature, the intention has been SS2PL.

SS2PL has been utilized to efficiently achieve Distributed and Global serializability since the 1980, and has become the de-facto standard for it.

SS2PL implementations have many variants.

It is also possible, but equally doubtful, that he actually shot down the hundreds of men with which his legend credits him.

Recognizing that the Rule of Law is `` a dynamic concept which should be employed not only to safeguard the civil and political rights of the individual in a free society '', the Congress asserted that it also included the responsibility `` to establish social, economic, educational and cultural conditions under which his legitimate aspirations and dignity may be realized ''.

At General Power's seat in the balcony there is also a gold phone.

In addition to the authentication and acknowledgment procedures which precede and follow the sending of the go messages, again in special codes, each message also contains an `` internal authenticator '', another specific signal to convince the recipient that he is getting the real thing.

He added that he also stresses the works of these favorite masters on tour, especially Mahler's First and Fourth symphonies, and Das Lied Von der Erde, and Bruckner's Sixth -- which is rarely played -- and Seventh.

The test of form is fidelity to the experience, a gauge also accepted by the abstract expressionist painters.

Though he is also concerned with freeing dance from pedestrian modes of activity, Merce Cunningham has selected a very different method for achieving his aim.

The answers derived by these means may determine not only the temporal organization of the dance but also its spatial design, special slips designating the location on the stage where the movement is to be performed.

It is because there is not only darkness but also light that our situation becomes inexplicable.

but there is also compassion.

also he is a drunk, and has lost his job on that account.

And if I have gone into so much detail about so small a work, that is because it is also so typical a work, representing the germinal form of a conflict which remains essential in Mann's writing: the crude sketch of Piepsam contains, in its critical, destructive and self-destructive tendencies, much that is enlarged and illuminated in the figures of, for instance, Naphta and Leverkuhn.

By `` image '' is meant not only a visual presentation, but also remembered sensations of any of the five senses plus the feelings which are immediately conjoined therewith.

he is questioning, also, every epistemology which stems from Hume's presupposition that experience is merely sense data in abstraction from causal efficacy, and that causal efficacy is something intellectually imputed to the world, not directly perceived.

it is true that they are also extremely dull.

Now the detective must save his own skin by informing on the girl he loves, who is also the real murderer.

But it is also the climax to one of the absorbing chapters in our current political history.

Since a civilizational crisis involves also a crisis in private interests and in the ruling class, reaction is normally found among those who feel themselves to be among the ruling class.

`` The Rocking Horse Winner '' is also a story about a boy's love for his mother.

Evidence is plentiful that early and later also he has been indebted to the Gothic romancers, who deal in extravagant horror, to the symbolists writing at the end of the preceding century, and in particular to the stream-of-consciousness novelists, Henry James and James Joyce among them.